Use internal wcstof instead of system wcstod in formcalc lexer

This CL switches the usage of wcstod to use the FXSYS_wcstof to
determine if a given string is a valid floating point number.

Using the internal method makes linux slightly slower (10's of ms)
makes mac a lot faster 900ms to 60ms for the test case in the bug.

The FXSYS_wcstof method has been extended to handle the parsing of
float exponents. Unittests were added for FXSYS_wcstof.

Bug: chromium:813646
Change-Id: Ie68287a336e3b95a0c0b845d5bf39db6fc82b39c
Reviewed-on: https://pdfium-review.googlesource.com/32510
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/core/fxcrt/fx_extension.cpp b/core/fxcrt/fx_extension.cpp
index 83aee86316..b1f2a95d62 100644
--- a/core/fxcrt/fx_extension.cpp
+++ b/core/fxcrt/fx_extension.cpp
@@ -50,6 +50,38 @@ float FXSYS_wcstof(const wchar_t* pwsStr, int32_t iLength, int32_t* pUsedLen) {
       fPrecise *= 0.1f;
     }
   }
+
+  if (iUsedLen < iLength &&
+      (pwsStr[iUsedLen] == 'e' || pwsStr[iUsedLen] == 'E')) {
+    ++iUsedLen;
+
+    bool negative_exponent = false;
+    if (iUsedLen < iLength &&
+        (pwsStr[iUsedLen] == '-' || pwsStr[iUsedLen] == '+')) {
+      negative_exponent = pwsStr[iUsedLen] == '-';
+      ++iUsedLen;
+    }
+
+    size_t exp_value = 0;
+    while (iUsedLen < iLength) {
+      wchar_t wch = pwsStr[iUsedLen];
+      if (!std::iswdigit(wch))
+        break;
+
+      exp_value = exp_value * 10.0f + (wch - L'0');
+      ++iUsedLen;
+    }
+
+    for (size_t i = exp_value; i > 0; --i) {
+      if (exp_value > 0) {
+        if (negative_exponent)
+          fValue /= 10;
+        else
+          fValue *= 10;
+      }
+    }
+  }
+
   if (pUsedLen)
     *pUsedLen = iUsedLen;