From c0450f609c5cc7a9720348b581a0134cb836c539 Mon Sep 17 00:00:00 2001
From: Spencer Lievens <spencerlievens@users.noreply.github.com>
Date: Tue, 9 May 2017 19:06:51 +0200
Subject: [PATCH] Improve EncodeBase58/DecodeBase58 performance (#1456)

* Improve DecodeBase58 performance

* Improve EncodeBase58
---
 src/base58.cpp | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/src/base58.cpp b/src/base58.cpp
index 7d69d33792839..b24da81e236b5 100644
--- a/src/base58.cpp
+++ b/src/base58.cpp
@@ -25,12 +25,14 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
         psz++;
     // Skip and count leading '1's.
     int zeroes = 0;
+    int length = 0;
     while (*psz == '1') {
         zeroes++;
         psz++;
     }
     // Allocate enough space in big-endian base256 representation.
-    std::vector<unsigned char> b256(strlen(psz) * 733 / 1000 + 1); // log(58) / log(256), rounded up.
+    int size = strlen(psz) * 733 /1000 + 1; // log(58) / log(256), rounded up.
+    std::vector<unsigned char> b256(size);
     // Process the characters.
     while (*psz && !isspace(*psz)) {
         // Decode base58 character
@@ -39,12 +41,14 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
             return false;
         // Apply "b256 = b256 * 58 + ch".
         int carry = ch - pszBase58;
-        for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); it != b256.rend(); it++) {
+        int i = 0;
+        for (std::vector<unsigned char>::reverse_iterator it = b256.rbegin(); (carry != 0 || i < length) && (it != b256.rend()); ++it, ++i) {
             carry += 58 * (*it);
             *it = carry % 256;
             carry /= 256;
         }
         assert(carry == 0);
+        length = i;
         psz++;
     }
     // Skip trailing spaces.
@@ -53,7 +57,7 @@ bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)
     if (*psz != 0)
         return false;
     // Skip leading zeroes in b256.
-    std::vector<unsigned char>::iterator it = b256.begin();
+    std::vector<unsigned char>::iterator it = b256.begin() + (size - length);
     while (it != b256.end() && *it == 0)
         it++;
     // Copy result into output vector.
@@ -68,26 +72,31 @@ std::string EncodeBase58(const unsigned char* pbegin, const unsigned char* pend)
 {
     // Skip & count leading zeroes.
     int zeroes = 0;
+    int length = 0;
     while (pbegin != pend && *pbegin == 0) {
         pbegin++;
         zeroes++;
     }
     // Allocate enough space in big-endian base58 representation.
-    std::vector<unsigned char> b58((pend - pbegin) * 138 / 100 + 1); // log(256) / log(58), rounded up.
+    int size = (pend - pbegin) * 138 / 100 + 1; // log(256) / log(58), rounded up.
+    std::vector<unsigned char> b58(size);
     // Process the bytes.
     while (pbegin != pend) {
         int carry = *pbegin;
+        int i = 0;
         // Apply "b58 = b58 * 256 + ch".
-        for (std::vector<unsigned char>::reverse_iterator it = b58.rbegin(); it != b58.rend(); it++) {
+        for (std::vector<unsigned char>::reverse_iterator it = b58.rbegin(); (carry != 0 || i < length) && (it != b58.rend()); it++, i++) {
             carry += 256 * (*it);
             *it = carry % 58;
             carry /= 58;
         }
+
         assert(carry == 0);
+        length = i;
         pbegin++;
     }
     // Skip leading zeroes in base58 result.
-    std::vector<unsigned char>::iterator it = b58.begin();
+    std::vector<unsigned char>::iterator it = b58.begin() + (size - length);
     while (it != b58.end() && *it == 0)
         it++;
     // Translate the result into a string.