Fix FXSYS_itoa() implementation.

core/src/fxcrt/fx_basic_gcc.cpp

Index: core/src/fxcrt/fx_basic_gcc.cpp
diff --git a/core/src/fxcrt/fx_basic_gcc.cpp b/core/src/fxcrt/fx_basic_gcc.cpp
index bf3d61524ec832d824b899bf16310660d702b464..6f17482156be7436f0e53e55243b2e1a63548202 100644
--- a/core/src/fxcrt/fx_basic_gcc.cpp
+++ b/core/src/fxcrt/fx_basic_gcc.cpp
@@ -32,30 +32,41 @@ T FXSYS_StrToInt(STR_T str) {
   }
   return neg ? -num : num;
 }
-template <typename T, typename STR_T>
+
+template <typename T, typename UT, typename STR_T>
 STR_T FXSYS_IntToStr(T value, STR_T string, int radix) {
-  int i = 0;
-  if (value < 0) {
-    string[i++] = '-';
-    value = -value;
-  } else if (value == 0) {
+  if (radix < 2 || radix > 16) {
+    string[0] = 0;
+    return string;
+  }
+  if (value == 0) {
     string[0] = '0';
     string[1] = 0;
     return string;
   }
+  int i = 0;
+  UT uvalue;
+  if (value < 0) {
+    string[i++] = '-';
+    // Standard trick to avoid undefined behaviour when negating INT_MIN.
+    uvalue = static_cast<UT>(-(value + 1)) + 1;
+  } else {
+    uvalue = value;
+  }
   int digits = 1;
-  T order = value / 10;
+  T order = uvalue / radix;
   while (order > 0) {
     digits++;
-    order = order / 10;
+    order = order / radix;
   }
   for (int d = digits - 1; d > -1; d--) {
-    string[d + i] = "0123456789abcdef"[value % 10];
-    value /= 10;
+    string[d + i] = "0123456789abcdef"[uvalue % radix];
+    uvalue /= radix;
   }
   string[digits + i] = 0;
   return string;
 }
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -72,10 +83,7 @@ int64_t FXSYS_wtoi64(const FX_WCHAR* str) {
   return FXSYS_StrToInt<int64_t, const FX_WCHAR*>(str);
 }
 const FX_CHAR* FXSYS_i64toa(int64_t value, FX_CHAR* str, int radix) {

[brucedawson, 2015/08/07 20:55:49]

I hate the design of passing in an FX_CHAR* and returning the same one, with no
way of verifying that the buffer is large enough.

If the sizes are standardized in pdfium then this could be improved by changing
the input parameter from "FX_CHAR* str" to "FXCHAR(&str)[34]" (for instance)
which would only compile if a 34 character buffer was passed.

The implementation function could remain as-is, but FXSYS_i64toa would be
changed. Any sites that were passing in a 34 character buffer would handle the
new prototype without needing changing.

Something to consider, for this change or for another.

-  return FXSYS_IntToStr<int64_t, FX_CHAR*>(value, str, radix);
-}
-const FX_WCHAR* FXSYS_i64tow(int64_t value, FX_WCHAR* str, int radix) {
-  return FXSYS_IntToStr<int64_t, FX_WCHAR*>(value, str, radix);
+  return FXSYS_IntToStr<int64_t, uint64_t, FX_CHAR*>(value, str, radix);
 }
 #ifdef __cplusplus
 }
@@ -182,7 +190,7 @@ int FXSYS_wcsicmp(const FX_WCHAR* dst, const FX_WCHAR* src) {
   return (f - l);
 }
 char* FXSYS_itoa(int value, char* string, int radix) {
-  return FXSYS_IntToStr<int32_t, FX_CHAR*>(value, string, radix);
+  return FXSYS_IntToStr<int32_t, uint32_t, FX_CHAR*>(value, string, radix);
 }
 #ifdef __cplusplus
 }