From 8c4df9033ce9fcc62044900e11a6e9e934869bd4 Mon Sep 17 00:00:00 2001
From: Yuri Gorshenin <y@maps.me>
Date: Fri, 18 Mar 2016 01:43:14 +0300
Subject: [PATCH] [base] Fixed integral to string conversion.

---
 base/base_tests/string_utils_test.cpp |  3 +++
 base/string_utils.hpp                 | 20 ++++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/base/base_tests/string_utils_test.cpp b/base/base_tests/string_utils_test.cpp
index 3f6dc94418..55b256bacf 100644
--- a/base/base_tests/string_utils_test.cpp
+++ b/base/base_tests/string_utils_test.cpp
@@ -253,6 +253,9 @@ UNIT_TEST(to_string)
 
   TEST_EQUAL(strings::to_string(123456789123456789ULL), "123456789123456789", ());
   TEST_EQUAL(strings::to_string(-987654321987654321LL), "-987654321987654321", ());
+
+  uint64_t const n = numeric_limits<uint64_t>::max();
+  TEST_EQUAL(strings::to_string(n), "18446744073709551615", ());
 }
 
 UNIT_TEST(to_string_dac)
diff --git a/base/string_utils.hpp b/base/string_utils.hpp
index 09f459d90c..4d006a0d08 100644
--- a/base/string_utils.hpp
+++ b/base/string_utils.hpp
@@ -223,6 +223,22 @@ template <typename T> string to_string(T t)
 
 namespace impl
 {
+template <typename T>
+int UpperBoundOnChars()
+{
+  // It's wrong to return just numeric_limits<T>::digits10 + [is
+  // signed] because digits10 for a type T is computed as:
+  //
+  // floor(log10(2 ^ (CHAR_BITS * sizeof(T)))) =
+  // floor(CHAR_BITS * sizeof(T) * log10(2))
+  //
+  // Therefore, due to rounding, we need to compensate possible
+  // error.
+  //
+  // NOTE: following code works only on two-complement systems!
+
+  return numeric_limits<T>::digits10 + is_signed<T>::value + 1;
+}
 
 template <typename T> char * to_string_digits(char * buf, T i)
 {
@@ -238,7 +254,7 @@ template <typename T> char * to_string_digits(char * buf, T i)
 template <typename T> string to_string_signed(T i)
 {
   bool const negative = i < 0;
-  int const sz = numeric_limits<T>::digits10 + 1;
+  int const sz = UpperBoundOnChars<T>();
   char buf[sz];
   char * end = buf + sz;
   char * beg = to_string_digits(end, negative ? -i : i);
@@ -252,7 +268,7 @@ template <typename T> string to_string_signed(T i)
 
 template <typename T> string to_string_unsigned(T i)
 {
-  int const sz = numeric_limits<T>::digits10;
+  int const sz = UpperBoundOnChars<T>();
   char buf[sz];
   char * end = buf + sz;
   char * beg = to_string_digits(end, i);