From 80f1a04d79b216b917c5b6d42f5b77084b426545 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sat, 6 Jul 2024 10:01:15 +0300
Subject: [PATCH 01/26] gh-102471: convert decimal module to use PyLongWriter
 API (PEP 757)

---
 Modules/_decimal/_decimal.c | 42 ++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 15 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index c564813036e504..5bc3cc26cc6363 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3639,12 +3639,13 @@ dec_format(PyObject *dec, PyObject *args)
 static PyObject *
 dec_as_long(PyObject *dec, PyObject *context, int round)
 {
-    PyLongObject *pylong;
+    PyObject *pylong;
     digit *ob_digit;
     size_t n;
     mpd_t *x;
     mpd_context_t workctx;
     uint32_t status = 0;
+    const PyLongLayout *layout = PyLong_GetNativeLayout();
 
     if (mpd_isspecial(MPD(dec))) {
         if (mpd_isnan(MPD(dec))) {
@@ -3672,34 +3673,45 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     status = 0;
-    ob_digit = NULL;
+
+    int64_t val = mpd_qget_i64(x, &status);
+    if (!status) {
+        mpd_del(x);
+        return PyLong_FromInt64(val);
+    }
+
+    n = (mpd_sizeinbase(x, 2) +
+         layout->bits_per_digit - 1) / layout->bits_per_digit;
+    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n,
+                                               (void**)&ob_digit);
+    /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
+    ob_digit[n-1] = 0;
+    if (writer == NULL) {
+        PyLongWriter_Discard(writer);
+        mpd_del(x);
+        return NULL;
+    }
+
+    status = 0;
 #if PYLONG_BITS_IN_DIGIT == 30
-    n = mpd_qexport_u32(&ob_digit, 0, PyLong_BASE, x, &status);
+    n = mpd_qexport_u32(&ob_digit, n, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    n = mpd_qexport_u16(&ob_digit, 0, PyLong_BASE, x, &status);
+    n = mpd_qexport_u16(&ob_digit, n, PyLong_BASE, x, &status);
 #else
     #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
 #endif
 
     if (n == SIZE_MAX) {
         PyErr_NoMemory();
+        PyLongWriter_Discard(writer);
         mpd_del(x);
         return NULL;
     }
 
-    if (n == 1) {
-        sdigit val = mpd_arith_sign(x) * ob_digit[0];
-        mpd_free(ob_digit);
-        mpd_del(x);
-        return PyLong_FromLong(val);
-    }
-
     assert(n > 0);
-    assert(!mpd_iszero(x));
-    pylong = _PyLong_FromDigits(mpd_isnegative(x), n, ob_digit);
-    mpd_free(ob_digit);
+    pylong = PyLongWriter_Finish(writer);
     mpd_del(x);
-    return (PyObject *) pylong;
+    return pylong;
 }
 
 /* Convert a Decimal to its exact integer ratio representation. */

From c13b7d23e6347ca8eaa4f8c8e287d433c7e76372 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sat, 14 Dec 2024 03:40:58 +0300
Subject: [PATCH 02/26] + news

---
 .../next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst  | 3 +++
 1 file changed, 3 insertions(+)
 create mode 100644 Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst

diff --git a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
new file mode 100644
index 00000000000000..2e91b4d60d1bc2
--- /dev/null
+++ b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
@@ -0,0 +1,3 @@
+Convert the :mod:`decimal` module to use :pep:`757` API.  That offer some
+speedup, if integer part of the :class:`~decimal.Decimal` instance is small.
+Patch by Sergey B Kirpichev.

From 589f926c01687833860f157ae88cbd8b6e5ccc45 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sat, 14 Dec 2024 03:44:02 +0300
Subject: [PATCH 03/26] Apply suggestions from code review
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Modules/_decimal/_decimal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 5bc3cc26cc6363..33c9d95e4a073f 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3680,8 +3680,8 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return PyLong_FromInt64(val);
     }
 
-    n = (mpd_sizeinbase(x, 2) +
-         layout->bits_per_digit - 1) / layout->bits_per_digit;
+    const uint8_t bpd = layout->bits_per_digit;
+    n = (mpd_sizeinbase(x, 2) + bpd - 1) / bpd;
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n,
                                                (void**)&ob_digit);
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */

From 6669b89214b1804ad0f3d76f8e9e3b61f6d41f33 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sat, 14 Dec 2024 09:43:16 +0300
Subject: [PATCH 04/26] + adapt dec_from_long() to use PEP 757

---
 Modules/_decimal/_decimal.c | 53 ++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 25 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 33c9d95e4a073f..4077c560d32654 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -30,7 +30,6 @@
 #endif
 
 #include <Python.h>
-#include "pycore_long.h"          // _PyLong_IsZero()
 #include "pycore_pystate.h"       // _PyThreadState_GET()
 #include "pycore_typeobject.h"
 #include "complexobject.h"
@@ -2323,38 +2322,42 @@ static PyObject *
 dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
               const mpd_context_t *ctx, uint32_t *status)
 {
-    PyObject *dec;
-    PyLongObject *l = (PyLongObject *)v;
+    PyObject *dec = PyDecType_New(state, type);
 
-    dec = PyDecType_New(state, type);
     if (dec == NULL) {
         return NULL;
     }
 
-    if (_PyLong_IsZero(l)) {
-        _dec_settriple(dec, MPD_POS, 0, 0);
-        return dec;
-    }
-
-    uint8_t sign = _PyLong_IsNegative(l) ? MPD_NEG :  MPD_POS;
+    PyLongExport export_long;
 
-    if (_PyLong_IsCompact(l)) {
-        _dec_settriple(dec, sign, l->long_value.ob_digit[0], 0);
-        mpd_qfinalize(MPD(dec), ctx, status);
-        return dec;
+    if (PyLong_Export(v, &export_long) == -1) {
+        Py_DECREF(dec);
+        return NULL;
     }
-    size_t len = _PyLong_DigitCount(l);
-
-#if PYLONG_BITS_IN_DIGIT == 30
-    mpd_qimport_u32(MPD(dec), l->long_value.ob_digit, len, sign, PyLong_BASE,
-                    ctx, status);
-#elif PYLONG_BITS_IN_DIGIT == 15
-    mpd_qimport_u16(MPD(dec), l->long_value.ob_digit, len, sign, PyLong_BASE,
-                    ctx, status);
-#else
-  #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
-#endif
+    if (export_long.digits) {
+        const PyLongLayout *layout = PyLong_GetNativeLayout();
+        const uint8_t bpd = layout->bits_per_digit;
+        const uint8_t sign = export_long.negative ? MPD_NEG :  MPD_POS;
+        const Py_ssize_t len = export_long.ndigits;
 
+        if (bpd == 30) {
+            mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
+                            1 << bpd, ctx, status);
+        }
+        else if (bpd == 15) {
+            mpd_qimport_u16(MPD(dec), export_long.digits, len, sign,
+                            1 << bpd, ctx, status);
+        }
+        else {
+            PyLong_FreeExport(&export_long);
+            Py_DECREF(dec);
+            return NULL;
+        }
+        PyLong_FreeExport(&export_long);
+    }
+    else {
+        mpd_qset_i64(MPD(dec), export_long.value, ctx, status);
+    }
     return dec;
 }
 

From 6e46bc1de119a5759c68401a05dd167ba5300cc7 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 10:56:54 +0300
Subject: [PATCH 05/26] Don't use PyLong_GetNativeLayout()

---
 Modules/_decimal/_decimal.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 4077c560d32654..a83cc7ce95bf89 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2335,24 +2335,18 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         return NULL;
     }
     if (export_long.digits) {
-        const PyLongLayout *layout = PyLong_GetNativeLayout();
-        const uint8_t bpd = layout->bits_per_digit;
         const uint8_t sign = export_long.negative ? MPD_NEG :  MPD_POS;
         const Py_ssize_t len = export_long.ndigits;
 
-        if (bpd == 30) {
-            mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
-                            1 << bpd, ctx, status);
-        }
-        else if (bpd == 15) {
-            mpd_qimport_u16(MPD(dec), export_long.digits, len, sign,
-                            1 << bpd, ctx, status);
-        }
-        else {
-            PyLong_FreeExport(&export_long);
-            Py_DECREF(dec);
-            return NULL;
-        }
+#if PYLONG_BITS_IN_DIGIT == 30
+        mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
+                        PyLong_BASE, ctx, status);
+#elif PYLONG_BITS_IN_DIGIT == 15
+        mpd_qimport_u16(MPD(dec), export_long.digits, len, sign,
+                        PyLong_BASE, ctx, status);
+#else
+  #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
+#endif
         PyLong_FreeExport(&export_long);
     }
     else {
@@ -3648,7 +3642,6 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     mpd_t *x;
     mpd_context_t workctx;
     uint32_t status = 0;
-    const PyLongLayout *layout = PyLong_GetNativeLayout();
 
     if (mpd_isspecial(MPD(dec))) {
         if (mpd_isnan(MPD(dec))) {
@@ -3683,8 +3676,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return PyLong_FromInt64(val);
     }
 
-    const uint8_t bpd = layout->bits_per_digit;
-    n = (mpd_sizeinbase(x, 2) + bpd - 1) / bpd;
+    n = (mpd_sizeinbase(x, 2) + PyLong_SHIFT - 1)/PyLong_SHIFT;
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n,
                                                (void**)&ob_digit);
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */

From 7f0061f249a0633cfc56daa4614ea5a4505993cf Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 11:53:33 +0300
Subject: [PATCH 06/26] Address review:

* cleanup: forgotten PyLongWriter_Discard, pylong variable
* clarify news
---
 .../C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst    | 6 +++---
 Modules/_decimal/_decimal.c                                 | 5 +----
 2 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
index 2e91b4d60d1bc2..93eb2e73d314fc 100644
--- a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
+++ b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
@@ -1,3 +1,3 @@
-Convert the :mod:`decimal` module to use :pep:`757` API.  That offer some
-speedup, if integer part of the :class:`~decimal.Decimal` instance is small.
-Patch by Sergey B Kirpichev.
+Convert the :mod:`decimal` module to use :pep:`757` C API (export-import
+integers).  That offer some speedup, if integer part of the
+:class:`~decimal.Decimal` instance is small.  Patch by Sergey B Kirpichev.
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index a83cc7ce95bf89..0c03a01139c3b3 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3636,7 +3636,6 @@ dec_format(PyObject *dec, PyObject *args)
 static PyObject *
 dec_as_long(PyObject *dec, PyObject *context, int round)
 {
-    PyObject *pylong;
     digit *ob_digit;
     size_t n;
     mpd_t *x;
@@ -3682,7 +3681,6 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
     ob_digit[n-1] = 0;
     if (writer == NULL) {
-        PyLongWriter_Discard(writer);
         mpd_del(x);
         return NULL;
     }
@@ -3704,9 +3702,8 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     assert(n > 0);
-    pylong = PyLongWriter_Finish(writer);
     mpd_del(x);
-    return pylong;
+    return PyLongWriter_Finish(writer);
 }
 
 /* Convert a Decimal to its exact integer ratio representation. */

From bae0234a265387ba195e520bff819a3b15abbdcf Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 13:22:28 +0300
Subject: [PATCH 07/26] Apply suggestions from code review
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 .../next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst   | 2 +-
 Modules/_decimal/_decimal.c                                     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
index 93eb2e73d314fc..c54c0f541ebd1e 100644
--- a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
+++ b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
@@ -1,3 +1,3 @@
 Convert the :mod:`decimal` module to use :pep:`757` C API (export-import
-integers).  That offer some speedup, if integer part of the
+integers).  That offer some speedup, if the integer part of the
 :class:`~decimal.Decimal` instance is small.  Patch by Sergey B Kirpichev.
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 0c03a01139c3b3..f26d953b7e040b 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2335,7 +2335,7 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         return NULL;
     }
     if (export_long.digits) {
-        const uint8_t sign = export_long.negative ? MPD_NEG :  MPD_POS;
+        const uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
         const Py_ssize_t len = export_long.ndigits;
 
 #if PYLONG_BITS_IN_DIGIT == 30

From 4e0460c80dd6021ecd154b5e27655e0ff28f07c3 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 16:46:53 +0300
Subject: [PATCH 08/26] address review: don't use digit type

---
 Modules/_decimal/_decimal.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index f26d953b7e040b..5d9e4bc1fb0c1b 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3636,7 +3636,7 @@ dec_format(PyObject *dec, PyObject *args)
 static PyObject *
 dec_as_long(PyObject *dec, PyObject *context, int round)
 {
-    digit *ob_digit;
+    void *digits;
     size_t n;
     mpd_t *x;
     mpd_context_t workctx;
@@ -3676,20 +3676,20 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     n = (mpd_sizeinbase(x, 2) + PyLong_SHIFT - 1)/PyLong_SHIFT;
-    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n,
-                                               (void**)&ob_digit);
-    /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
-    ob_digit[n-1] = 0;
+    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n, &digits);
     if (writer == NULL) {
         mpd_del(x);
         return NULL;
     }
 
     status = 0;
+    /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
 #if PYLONG_BITS_IN_DIGIT == 30
-    n = mpd_qexport_u32(&ob_digit, n, PyLong_BASE, x, &status);
+    memset(digits + sizeof(uint32_t)*(n - 1), 0, sizeof(uint32_t));
+    n = mpd_qexport_u32((uint32_t **)&digits, n, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    n = mpd_qexport_u16(&ob_digit, n, PyLong_BASE, x, &status);
+    memset(digits + sizeof(unit16_t)*(n - 1), 0, sizeof(uint16_t));
+    n = mpd_qexport_u16((uint16_t **)&digits, n, PyLong_BASE, x, &status);
 #else
     #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
 #endif

From 87ded2e8c779d41d48e071547a893ddeb3781af6 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 17:00:49 +0300
Subject: [PATCH 09/26] + forgot (char*) cast

---
 Modules/_decimal/_decimal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 5d9e4bc1fb0c1b..4d18326cdccd83 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3685,10 +3685,10 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     status = 0;
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
 #if PYLONG_BITS_IN_DIGIT == 30
-    memset(digits + sizeof(uint32_t)*(n - 1), 0, sizeof(uint32_t));
+    memset((char *)digits + sizeof(uint32_t)*(n - 1), 0, sizeof(uint32_t));
     n = mpd_qexport_u32((uint32_t **)&digits, n, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    memset(digits + sizeof(unit16_t)*(n - 1), 0, sizeof(uint16_t));
+    memset((char *)digits + sizeof(uint16_t)*(n - 1), 0, sizeof(uint16_t));
     n = mpd_qexport_u16((uint16_t **)&digits, n, PyLong_BASE, x, &status);
 #else
     #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"

From 541441e706bbe4a1f740235ed8baae69f4ae7008 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Mon, 16 Dec 2024 18:24:44 +0300
Subject: [PATCH 10/26] Apply Serhiy suggestion

---
 Modules/_decimal/_decimal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 4d18326cdccd83..eace46b9beb632 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3685,10 +3685,10 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     status = 0;
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
 #if PYLONG_BITS_IN_DIGIT == 30
-    memset((char *)digits + sizeof(uint32_t)*(n - 1), 0, sizeof(uint32_t));
+    ((uint32_t *)digits)[n - 1] = 0;
     n = mpd_qexport_u32((uint32_t **)&digits, n, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    memset((char *)digits + sizeof(uint16_t)*(n - 1), 0, sizeof(uint16_t));
+    ((uint16_t *)digits)[n - 1] = 0;
     n = mpd_qexport_u16((uint16_t **)&digits, n, PyLong_BASE, x, &status);
 #else
     #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"

From 6ab20f10a969cfd25eb0d316beddf72e5bf3d0a2 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 17 Dec 2024 05:02:51 +0300
Subject: [PATCH 11/26] add asserts

---
 Modules/_decimal/_decimal.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index eace46b9beb632..8a0938236b5b84 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3675,8 +3675,8 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return PyLong_FromInt64(val);
     }
 
-    n = (mpd_sizeinbase(x, 2) + PyLong_SHIFT - 1)/PyLong_SHIFT;
-    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n, &digits);
+    size_t len = mpd_sizeinbase(x, PyLong_BASE);
+    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);
     if (writer == NULL) {
         mpd_del(x);
         return NULL;
@@ -3685,14 +3685,15 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     status = 0;
     /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
 #if PYLONG_BITS_IN_DIGIT == 30
-    ((uint32_t *)digits)[n - 1] = 0;
-    n = mpd_qexport_u32((uint32_t **)&digits, n, PyLong_BASE, x, &status);
+    ((uint32_t *)digits)[len - 1] = 0;
+    n = mpd_qexport_u32((uint32_t **)&digits, len, PyLong_BASE, x, &status);
 #elif PYLONG_BITS_IN_DIGIT == 15
-    ((uint16_t *)digits)[n - 1] = 0;
-    n = mpd_qexport_u16((uint16_t **)&digits, n, PyLong_BASE, x, &status);
+    ((uint16_t *)digits)[len - 1] = 0;
+    n = mpd_qexport_u16((uint16_t **)&digits, len, PyLong_BASE, x, &status);
 #else
     #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
 #endif
+    assert(n == len || n == len - 1);
 
     if (n == SIZE_MAX) {
         PyErr_NoMemory();

From 83471fdbe58a1ffa857359684e57c805e0ccbddf Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 17 Dec 2024 09:19:26 +0300
Subject: [PATCH 12/26] speed up export

---
 Modules/_decimal/_decimal.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 8a0938236b5b84..2b246c7d9cd80d 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2350,7 +2350,16 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         PyLong_FreeExport(&export_long);
     }
     else {
-        mpd_qset_i64(MPD(dec), export_long.value, ctx, status);
+        const int64_t value = export_long.value;
+
+        if (INT32_MIN <= value && value <= INT32_MAX) {
+            _dec_settriple(dec, value < 0 ? MPD_NEG : MPD_POS,
+                           Py_ABS(value), 0);
+            mpd_qfinalize(MPD(dec), ctx, status);
+        }
+        else {
+            mpd_qset_i64(MPD(dec), value, ctx, status);
+        }
     }
     return dec;
 }

From cb169f7b5dfac4908f987453e94a4bf2766a5906 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 17 Dec 2024 15:38:29 +0300
Subject: [PATCH 13/26] Apply suggestions from code review

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Modules/_decimal/_decimal.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 2b246c7d9cd80d..a13cfdd175f10a 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2352,9 +2352,9 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
     else {
         const int64_t value = export_long.value;
 
-        if (INT32_MIN <= value && value <= INT32_MAX) {
+        if (-UINT32_MAX <= value && value <= UINT32_MAX) {
             _dec_settriple(dec, value < 0 ? MPD_NEG : MPD_POS,
-                           Py_ABS(value), 0);
+                           (uint32_t)Py_ABS(value), 0);
             mpd_qfinalize(MPD(dec), ctx, status);
         }
         else {

From 61e76d2aaab98d4b0397e749e33c2e2c7abf82e4 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Thu, 19 Dec 2024 06:54:51 +0300
Subject: [PATCH 14/26] use PyLong_GetNativeLayout() to query layout

---
 Modules/_decimal/_decimal.c | 42 +++++++++++++++++++------------------
 1 file changed, 22 insertions(+), 20 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index a13cfdd175f10a..f302cc77f9fff6 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2335,18 +2335,19 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         return NULL;
     }
     if (export_long.digits) {
+        const PyLongLayout *layout = PyLong_GetNativeLayout();
+        const uint32_t base = 1 << layout->bits_per_digit;
         const uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
         const Py_ssize_t len = export_long.ndigits;
 
-#if PYLONG_BITS_IN_DIGIT == 30
-        mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
-                        PyLong_BASE, ctx, status);
-#elif PYLONG_BITS_IN_DIGIT == 15
-        mpd_qimport_u16(MPD(dec), export_long.digits, len, sign,
-                        PyLong_BASE, ctx, status);
-#else
-  #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
-#endif
+        if (base > UINT16_MAX) {
+            mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
+                            base, ctx, status);
+        }
+        else {
+            mpd_qimport_u16(MPD(dec), export_long.digits, len, sign,
+                            base, ctx, status);
+        }
         PyLong_FreeExport(&export_long);
     }
     else {
@@ -3684,7 +3685,9 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return PyLong_FromInt64(val);
     }
 
-    size_t len = mpd_sizeinbase(x, PyLong_BASE);
+    const PyLongLayout *layout = PyLong_GetNativeLayout();
+    const uint32_t base = 1 << layout->bits_per_digit;
+    size_t len = mpd_sizeinbase(x, base);
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);
     if (writer == NULL) {
         mpd_del(x);
@@ -3692,16 +3695,15 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     status = 0;
-    /* mpd_sizeinbase can overestimate size by 1 digit, set it to zero. */
-#if PYLONG_BITS_IN_DIGIT == 30
-    ((uint32_t *)digits)[len - 1] = 0;
-    n = mpd_qexport_u32((uint32_t **)&digits, len, PyLong_BASE, x, &status);
-#elif PYLONG_BITS_IN_DIGIT == 15
-    ((uint16_t *)digits)[len - 1] = 0;
-    n = mpd_qexport_u16((uint16_t **)&digits, len, PyLong_BASE, x, &status);
-#else
-    #error "PYLONG_BITS_IN_DIGIT should be 15 or 30"
-#endif
+    /* mpd_sizeinbase can overestimate size by 1 digit, set it first to zero. */
+    if (base > UINT16_MAX) {
+        ((uint32_t *)digits)[len - 1] = 0;
+        n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
+    }
+    else {
+        ((uint16_t *)digits)[len - 1] = 0;
+        n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
+    }
     assert(n == len || n == len - 1);
 
     if (n == SIZE_MAX) {

From 90bafc1a35e5e9a4d5ac18692b8abc38370c348a Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Thu, 19 Dec 2024 12:37:11 +0300
Subject: [PATCH 15/26] + comment

---
 Modules/_decimal/_decimal.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index f302cc77f9fff6..79973a668433d3 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3704,6 +3704,8 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         ((uint16_t *)digits)[len - 1] = 0;
         n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
     }
+    /* mpd_qexport_*() functions above used with assumption, that no
+       resizing occur, i.e. len was obtained by a call to mpd_sizeinbase. */
     assert(n == len || n == len - 1);
 
     if (n == SIZE_MAX) {

From c117956c8f0893539d683c6cbd87701d5195566a Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Thu, 19 Dec 2024 14:51:01 +0300
Subject: [PATCH 16/26] Apply suggestions from code review

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Modules/_decimal/_decimal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 79973a668433d3..891e001586a32b 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2336,7 +2336,7 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
     }
     if (export_long.digits) {
         const PyLongLayout *layout = PyLong_GetNativeLayout();
-        const uint32_t base = 1 << layout->bits_per_digit;
+        const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
         const uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
         const Py_ssize_t len = export_long.ndigits;
 
@@ -2353,7 +2353,7 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
     else {
         const int64_t value = export_long.value;
 
-        if (-UINT32_MAX <= value && value <= UINT32_MAX) {
+        if (-(int64_t)UINT32_MAX <= value && value <= (int64_t)UINT32_MAX) {
             _dec_settriple(dec, value < 0 ? MPD_NEG : MPD_POS,
                            (uint32_t)Py_ABS(value), 0);
             mpd_qfinalize(MPD(dec), ctx, status);
@@ -3686,7 +3686,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     const PyLongLayout *layout = PyLong_GetNativeLayout();
-    const uint32_t base = 1 << layout->bits_per_digit;
+    const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
     size_t len = mpd_sizeinbase(x, base);
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);
     if (writer == NULL) {

From 7b97855a752d76250ad346a4f58c3f63b8fb3f16 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Fri, 20 Dec 2024 05:55:55 +0300
Subject: [PATCH 17/26] address review:

* move comment up
* move assert down
* remove redundant assert & restore nonzero assert
---
 Modules/_decimal/_decimal.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 891e001586a32b..31bb7b798cb38d 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3684,6 +3684,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         mpd_del(x);
         return PyLong_FromInt64(val);
     }
+    assert(!mpd_iszero(x));
 
     const PyLongLayout *layout = PyLong_GetNativeLayout();
     const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
@@ -3695,7 +3696,9 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     status = 0;
-    /* mpd_sizeinbase can overestimate size by 1 digit, set it first to zero. */
+    /* mpd_qexport_*() functions used here with assumption, that no resizing
+       occur, i.e. len was obtained by a call to mpd_sizeinbase.  Note that
+       it can overestimate size by 1 digit, so set it first to zero. */
     if (base > UINT16_MAX) {
         ((uint32_t *)digits)[len - 1] = 0;
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
@@ -3704,9 +3707,6 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         ((uint16_t *)digits)[len - 1] = 0;
         n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
     }
-    /* mpd_qexport_*() functions above used with assumption, that no
-       resizing occur, i.e. len was obtained by a call to mpd_sizeinbase. */
-    assert(n == len || n == len - 1);
 
     if (n == SIZE_MAX) {
         PyErr_NoMemory();
@@ -3715,7 +3715,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return NULL;
     }
 
-    assert(n > 0);
+    assert(n == len || n == len - 1);
     mpd_del(x);
     return PyLongWriter_Finish(writer);
 }

From 7e0e9a9826c67d96a17f4977f8209d15a56fece9 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sun, 22 Dec 2024 17:10:40 +0300
Subject: [PATCH 18/26] Update
 Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 .../next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
index c54c0f541ebd1e..6cf5fd2872cd43 100644
--- a/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
+++ b/Misc/NEWS.d/next/C_API/2024-12-14-03-40-15.gh-issue-127925.FF7aov.rst
@@ -1,3 +1,3 @@
 Convert the :mod:`decimal` module to use :pep:`757` C API (export-import
-integers).  That offer some speedup, if the integer part of the
+integers), offering some speed-up if the integer part of the
 :class:`~decimal.Decimal` instance is small.  Patch by Sergey B Kirpichev.

From 5a00ee2f1d27ac539129987b3d11fa3e0935a34f Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Thu, 26 Dec 2024 09:41:08 +0300
Subject: [PATCH 19/26] set all digits to 0

---
 Modules/_decimal/_decimal.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 31bb7b798cb38d..6df517698d7980 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3697,14 +3697,14 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
 
     status = 0;
     /* mpd_qexport_*() functions used here with assumption, that no resizing
-       occur, i.e. len was obtained by a call to mpd_sizeinbase.  Note that
-       it can overestimate size by 1 digit, so set it first to zero. */
+       occur, i.e. len was obtained by a call to mpd_sizeinbase.  Set digits
+       to zero, as size can be overestimated. */
     if (base > UINT16_MAX) {
-        ((uint32_t *)digits)[len - 1] = 0;
+        memset(digits, 0, len*sizeof(uint32_t));
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
     }
     else {
-        ((uint16_t *)digits)[len - 1] = 0;
+        memset(digits, 0, len*sizeof(uint16_t));
         n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
     }
 

From f6a4afb08e96087471c4d6da19ae6e601c42078e Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 7 Jan 2025 05:02:11 +0300
Subject: [PATCH 20/26] + cleanup, add asserts

---
 Modules/_decimal/_decimal.c | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index bd323ba1fca147..dc9e901c8c8c91 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3642,12 +3642,6 @@ dec_format(PyObject *dec, PyObject *args)
 static PyObject *
 dec_as_long(PyObject *dec, PyObject *context, int round)
 {
-    void *digits;
-    size_t n;
-    mpd_t *x;
-    mpd_context_t workctx;
-    uint32_t status = 0;
-
     if (mpd_isspecial(MPD(dec))) {
         if (mpd_isnan(MPD(dec))) {
             PyErr_SetString(PyExc_ValueError,
@@ -3660,12 +3654,16 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return NULL;
     }
 
-    x = mpd_qnew();
+    mpd_t *x = mpd_qnew();
+
     if (x == NULL) {
         PyErr_NoMemory();
         return NULL;
     }
-    workctx = *CTX(context);
+
+    mpd_context_t workctx = *CTX(context);
+    uint32_t status = 0;
+
     workctx.round = round;
     mpd_qround_to_int(x, MPD(dec), &workctx, &status);
     if (dec_addstatus(context, status)) {
@@ -3674,8 +3672,8 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     status = 0;
-
     int64_t val = mpd_qget_i64(x, &status);
+
     if (!status) {
         mpd_del(x);
         return PyLong_FromInt64(val);
@@ -3684,8 +3682,16 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
 
     const PyLongLayout *layout = PyLong_GetNativeLayout();
     const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
-    size_t len = mpd_sizeinbase(x, base);
+
+    assert(layout->bits_per_digit <= 32);
+    assert(layout->digits_order == -1);
+    assert(layout->digit_endianness == (PY_LITTLE_ENDIAN ? -1 : 1));
+    assert(layout->digit_size == 2 || layout->digit_size == 4);
+
+    size_t n, len = mpd_sizeinbase(x, base);
+    void *digits;
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);
+
     if (writer == NULL) {
         mpd_del(x);
         return NULL;
@@ -3695,7 +3701,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     /* mpd_qexport_*() functions used here with assumption, that no resizing
        occur, i.e. len was obtained by a call to mpd_sizeinbase.  Set digits
        to zero, as size can be overestimated. */
-    if (base > UINT16_MAX) {
+    if (layout->digit_size == 4) {
         memset(digits, 0, len*sizeof(uint32_t));
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
     }

From 0fec6e17bba3c3fdcf405dafb44972aa7b83c248 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 7 Jan 2025 14:15:29 +0300
Subject: [PATCH 21/26] address review

---
 Modules/_decimal/_decimal.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index dc9e901c8c8c91..79f4f56521d07f 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2340,7 +2340,7 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
         uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
         Py_ssize_t len = export_long.ndigits;
 
-        assert(layout->bits_per_digit <= 32);
+        assert(layout->bits_per_digit < 32);
         assert(layout->digits_order == -1);
         assert(layout->digit_endianness == (PY_LITTLE_ENDIAN ? -1 : 1));
         assert(layout->digit_size == 2 || layout->digit_size == 4);
@@ -3681,9 +3681,9 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     assert(!mpd_iszero(x));
 
     const PyLongLayout *layout = PyLong_GetNativeLayout();
-    const uint32_t base = (uint32_t)1 << layout->bits_per_digit;
+    uint32_t base = (uint32_t)1 << layout->bits_per_digit;
 
-    assert(layout->bits_per_digit <= 32);
+    assert(layout->bits_per_digit < 32);
     assert(layout->digits_order == -1);
     assert(layout->digit_endianness == (PY_LITTLE_ENDIAN ? -1 : 1));
     assert(layout->digit_size == 2 || layout->digit_size == 4);
@@ -3702,11 +3702,11 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
        occur, i.e. len was obtained by a call to mpd_sizeinbase.  Set digits
        to zero, as size can be overestimated. */
     if (layout->digit_size == 4) {
-        memset(digits, 0, len*sizeof(uint32_t));
+        memset(digits, 0, 4*len);
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
     }
     else {
-        memset(digits, 0, len*sizeof(uint16_t));
+        memset(digits, 0, 2*len);
         n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
     }
 
@@ -3717,7 +3717,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
         return NULL;
     }
 
-    assert(n == len || n == len - 1);
+    assert(n <= len);
     mpd_del(x);
     return PyLongWriter_Finish(writer);
 }

From 59636f9259d8b70d304ba8a57c011315f23a084b Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Tue, 7 Jan 2025 15:10:20 +0300
Subject: [PATCH 22/26] address review

---
 Modules/_decimal/_decimal.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 79f4f56521d07f..e6e608639f4c5f 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -2336,15 +2336,16 @@ dec_from_long(decimal_state *state, PyTypeObject *type, PyObject *v,
     }
     if (export_long.digits) {
         const PyLongLayout *layout = PyLong_GetNativeLayout();
-        uint32_t base = (uint32_t)1 << layout->bits_per_digit;
-        uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
-        Py_ssize_t len = export_long.ndigits;
 
         assert(layout->bits_per_digit < 32);
         assert(layout->digits_order == -1);
         assert(layout->digit_endianness == (PY_LITTLE_ENDIAN ? -1 : 1));
         assert(layout->digit_size == 2 || layout->digit_size == 4);
 
+        uint32_t base = (uint32_t)1 << layout->bits_per_digit;
+        uint8_t sign = export_long.negative ? MPD_NEG : MPD_POS;
+        Py_ssize_t len = export_long.ndigits;
+
         if (layout->digit_size == 4) {
             mpd_qimport_u32(MPD(dec), export_long.digits, len, sign,
                             base, ctx, status);
@@ -3681,13 +3682,13 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     assert(!mpd_iszero(x));
 
     const PyLongLayout *layout = PyLong_GetNativeLayout();
-    uint32_t base = (uint32_t)1 << layout->bits_per_digit;
 
     assert(layout->bits_per_digit < 32);
     assert(layout->digits_order == -1);
     assert(layout->digit_endianness == (PY_LITTLE_ENDIAN ? -1 : 1));
     assert(layout->digit_size == 2 || layout->digit_size == 4);
 
+    uint32_t base = (uint32_t)1 << layout->bits_per_digit;
     size_t n, len = mpd_sizeinbase(x, base);
     void *digits;
     PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);

From b8bf49ff0731b8220ae5061da8ce31eb0f11d538 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Wed, 8 Jan 2025 05:36:06 +0300
Subject: [PATCH 23/26] Update Modules/_decimal/_decimal.c

Co-authored-by: Victor Stinner <vstinner@python.org>
---
 Modules/_decimal/_decimal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index e6e608639f4c5f..0689db5cd09e1c 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3701,7 +3701,7 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     status = 0;
     /* mpd_qexport_*() functions used here with assumption, that no resizing
        occur, i.e. len was obtained by a call to mpd_sizeinbase.  Set digits
-       to zero, as size can be overestimated. */
+       to zero, as len can be overestimated. */
     if (layout->digit_size == 4) {
         memset(digits, 0, 4*len);
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);

From a8189e62b8914acf55732386dea5a770e5e16ed2 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Sun, 12 Jan 2025 04:07:50 +0300
Subject: [PATCH 24/26] Update Modules/_decimal/_decimal.c
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
---
 Modules/_decimal/_decimal.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 0689db5cd09e1c..c14b1b05bd1007 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3699,9 +3699,9 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     }
 
     status = 0;
-    /* mpd_qexport_*() functions used here with assumption, that no resizing
-       occur, i.e. len was obtained by a call to mpd_sizeinbase.  Set digits
-       to zero, as len can be overestimated. */
+    /* The mpd_qexport_*() functions used here assume that no resizing occurs,
+       that is, 'len' was obtained via mpd_sizeinbase().  We also fill 'digits'
+       with zeros first since 'len' can be overestimated. */
     if (layout->digit_size == 4) {
         memset(digits, 0, 4*len);
         n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);

From 336e881229d57de722ca451bf7d05e7e703800c7 Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Fri, 24 Jan 2025 06:58:11 +0300
Subject: [PATCH 25/26] use temporary buffer of digits, tmp_digits

---
 Modules/_decimal/_decimal.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index c14b1b05bd1007..d04ebe036c325a 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3689,37 +3689,34 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     assert(layout->digit_size == 2 || layout->digit_size == 4);
 
     uint32_t base = (uint32_t)1 << layout->bits_per_digit;
-    size_t n, len = mpd_sizeinbase(x, base);
-    void *digits;
-    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), len, &digits);
-
-    if (writer == NULL) {
-        mpd_del(x);
-        return NULL;
-    }
+    void *tmp_digits = NULL;
+    size_t n;
 
     status = 0;
-    /* The mpd_qexport_*() functions used here assume that no resizing occurs,
-       that is, 'len' was obtained via mpd_sizeinbase().  We also fill 'digits'
-       with zeros first since 'len' can be overestimated. */
     if (layout->digit_size == 4) {
-        memset(digits, 0, 4*len);
-        n = mpd_qexport_u32((uint32_t **)&digits, len, base, x, &status);
+        n = mpd_qexport_u32((uint32_t **)&tmp_digits, 0, base, x, &status);
     }
     else {
-        memset(digits, 0, 2*len);
-        n = mpd_qexport_u16((uint16_t **)&digits, len, base, x, &status);
+        n = mpd_qexport_u16((uint16_t **)&tmp_digits, 0, base, x, &status);
     }
 
     if (n == SIZE_MAX) {
         PyErr_NoMemory();
-        PyLongWriter_Discard(writer);
         mpd_del(x);
+        mpd_free(tmp_digits);
         return NULL;
     }
 
-    assert(n <= len);
+    void *digits;
+    PyLongWriter *writer = PyLongWriter_Create(mpd_isnegative(x), n, &digits);
+
     mpd_del(x);
+    if (writer == NULL) {
+        mpd_free(tmp_digits);
+        return NULL;
+    }
+    memcpy(digits, tmp_digits, layout->digit_size*n);
+    mpd_free(tmp_digits);
     return PyLongWriter_Finish(writer);
 }
 

From e658f2b86a3da4d26f61054edc5c912f6cb8ad4d Mon Sep 17 00:00:00 2001
From: Sergey B Kirpichev <skirpichev@gmail.com>
Date: Fri, 24 Jan 2025 13:42:31 +0300
Subject: [PATCH 26/26] address review: comment

---
 Modules/_decimal/_decimal.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index d04ebe036c325a..b9abd8bd2e7a53 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -3689,6 +3689,11 @@ dec_as_long(PyObject *dec, PyObject *context, int round)
     assert(layout->digit_size == 2 || layout->digit_size == 4);
 
     uint32_t base = (uint32_t)1 << layout->bits_per_digit;
+    /* We use a temporary buffer for digits for now, as for nonzero rdata
+       mpd_qexport_u32/u16() require either space "allocated by one of
+       libmpdec’s allocation functions" or "rlen MUST be correct" (to avoid
+       reallocation).  This can be further optimized by using rlen from
+       mpd_sizeinbase().  See gh-127925. */
     void *tmp_digits = NULL;
     size_t n;