Added strxfrm

strxfrm transforms a string src into a string dest such that calling
strcmp(dest1, dest2) is same as calling strcoll(src1, src2). strxfrm
calls strlcpy internally because cosmopolitan libc does not support
locales. Also added the unlicensing declaration at the start of the
file.

libc/str/str.h

@@ -156,6 +156,7 @@ char16_t *strcat16(char16_t *, const char16_t *) memcpyesque;
 wchar_t *wcscat(wchar_t *, const wchar_t *) memcpyesque;
 size_t strlcpy(char *, const char *, size_t);
 size_t strlcat(char *, const char *, size_t);
+size_t strxfrm(char *, const char *, size_t);
 char *strcpy(char *, const char *) memcpyesque;
 char16_t *strcpy16(char16_t *, const char16_t *) memcpyesque;
 wchar_t *wcscpy(wchar_t *, const wchar_t *) memcpyesque;

libc/str/strxfrm.c

@@ -0,0 +1,48 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ This is free and unencumbered software released into the public domain.      │
+│                                                                              │
+│ Anyone is free to copy, modify, publish, use, compile, sell, or              │
+│ distribute this software, either in source code form or as a compiled        │
+│ binary, for any purpose, commercial or non-commercial, and by any            │
+│ means.                                                                       │
+│                                                                              │
+│ In jurisdictions that recognize copyright laws, the author or authors        │
+│ of this software dedicate any and all copyright interest in the              │
+│ software to the public domain. We make this dedication for the benefit       │
+│ of the public at large and to the detriment of our heirs and                 │
+│ successors. We intend this dedication to be an overt act of                  │
+│ relinquishment in perpetuity of all present and future rights to this        │
+│ software under copyright law.                                                │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,              │
+│ EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF           │
+│ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.       │
+│ IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR            │
+│ OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,        │
+│ ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR        │
+│ OTHER DEALINGS IN THE SOFTWARE.                                              │
+│                                                                              │
+╚─────────────────────────────────────────────────────────────────────────────*/
+
+#include "libc/assert.h"
+#include "libc/str/str.h"
+
+/**
+ * transforms strings into the current C locale.
+ * calling strcmp() on two strxfrm()-ed strings
+ * is same as calling strcoll() on the originals.
+ *
+ * @param dest is buffer which needn't be initialized
+ * @param src is a NUL-terminated string
+ * @param count is number of bytes to write to destination
+ * @return length of transformed string
+ * @note dest and src can't overlap
+ * @note dest array size should be greater than count
+ * @note if dest is NULL, count has to be zero
+ */
+size_t strxfrm(char *dest, const char *src, size_t count) {
+  assert(dest == NULL ? count == 0 : 1);
+  return strlcpy(dest, src, count);
+}