Bug 608915 - part 2 - use MFBT's double-conversion code in nsString::AppendFloat; r=bz,gps

xpcom/string/public/nsTSubstring.h

@@ -445,12 +445,8 @@ class nsTSubstring_CharT
       /**
        * Append the given float to this string 
        */
-      void AppendFloat( float aFloat )
-                      { DoAppendFloat(aFloat, 6); }
-      void AppendFloat( double aFloat )
-                      { DoAppendFloat(aFloat, 15); }
-  private:
-      void NS_FASTCALL DoAppendFloat( double aFloat, int digits );
+      void NS_FASTCALL AppendFloat( float aFloat );
+      void NS_FASTCALL AppendFloat( double aFloat );
   public:
 
     // AppendLiteral must ONLY be applied to an actual literal string.

xpcom/string/src/moz.build

@@ -25,6 +25,10 @@ if CONFIG['INTEL_ARCHITECTURE']:
         'nsUTF8UtilsSSE2.cpp',
     ]
 
+LOCAL_INCLUDES += [
+    '/mfbt/double-conversion',
+]
+
 LIBRARY_NAME = 'string_s'
 
 MSVC_ENABLE_PGO = True

xpcom/string/src/nsTSubstring.cpp

@@ -4,7 +4,9 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "mozilla/MemoryReporting.h"
-#include "prdtoa.h"
+#include "double-conversion.h"
+
+using double_conversion::DoubleToStringConverter;
 
 #ifdef XPCOM_STRING_CONSTRUCTOR_OUT_OF_LINE
 nsTSubstring_CharT::nsTSubstring_CharT( char_type *data, size_type length,
@@ -790,103 +792,94 @@ void nsTSubstring_CharT::AppendPrintf( const char* format, va_list ap )
       NS_RUNTIMEABORT("Allocation or other failure in PR_vsxprintf");
   }
 
-/* hack to make sure we define Modified_cnvtf only once */
+/* hack to make sure we define FormatWithoutTrailingZeros only once */
 #ifdef CharT_is_PRUnichar
-/**
- * This is a copy of |PR_cnvtf| with a bug fixed.  (The second argument
- * of PR_dtoa is 2 rather than 1.)
- *
- * XXX(darin): if this is the right thing, then why wasn't it fixed in NSPR?!?
- */
-static void 
-Modified_cnvtf(char (& buf)[40], int prcsn, double fval)
+// Returns the length of the formatted aDouble in buf.
+static int
+FormatWithoutTrailingZeros(char (& buf)[40], double aDouble,
+                           int precision)
 {
-  int decpt, sign, numdigits;
-  char num[40];
-  char *nump;
-  char *bufp = buf;
-  char *endnum;
+  static const DoubleToStringConverter converter(DoubleToStringConverter::UNIQUE_ZERO |
+                                                 DoubleToStringConverter::EMIT_POSITIVE_EXPONENT_SIGN,
+                                                 "Infinity",
+                                                 "NaN",
+                                                 'e',
+                                                 -6, 21,
+                                                 6, 1);
+  double_conversion::StringBuilder builder(buf, sizeof(buf));
+  bool exponential_notation = false;
+  converter.ToPrecision(aDouble, precision, &exponential_notation, &builder);
+  int length = builder.position();
+  char* formattedDouble = builder.Finalize();
 
-  if (PR_dtoa(fval, 2, prcsn, &decpt, &sign, &endnum, num, sizeof(num))
-      == PR_FAILURE) {
-    buf[0] = '\0';
-    return;
+  // If we have a shorter string than precision, it means we have a special
+  // value (NaN or Infinity).  All other numbers will be formatted with at
+  // least precision digits.
+  if (length <= precision) {
+    return length;
   }
-  numdigits = endnum - num;
-  nump = num;
-
-  /*
-   * The NSPR code had a fancy way of checking that we weren't dealing
-   * with -0.0 or -NaN, but I'll just use < instead.
-   * XXX Should we check !isnan(fval) as well?  Is it portable?  We
-   * probably don't need to bother since NAN isn't portable.
-   */
-  if (sign && fval < 0.0f) {
-    *bufp++ = '-';
+    
+  char* end = formattedDouble + length;
+  char* decimalPoint = strchr(buf, '.');
+  // No trailing zeros to remove.
+  if (decimalPoint == nullptr) {
+    return length;
   }
 
-  if (decpt == 9999) {
-    while ((*bufp++ = *nump++) != 0) {} /* nothing to execute */
-    return;
-  }
-
-  if (decpt > (prcsn+1) || decpt < -(prcsn-1) || decpt < -5) {
-    *bufp++ = *nump++;
-    if (numdigits != 1) {
-      *bufp++ = '.';
-    }
-
-    while (*nump != '\0') {
-      *bufp++ = *nump++;
-    }
-    *bufp++ = 'e';
-    PR_snprintf(bufp, sizeof(num) - (bufp - buf), "%+d", decpt-1);
-  }
-  else if (decpt >= 0) {
-    if (decpt == 0) {
-      *bufp++ = '0';
-    }
-    else {
-      while (decpt--) {
-        if (*nump != '\0') {
-          *bufp++ = *nump++;
-        }
-        else {
-          *bufp++ = '0';
-        }
+  if (MOZ_UNLIKELY(exponential_notation)) {
+    // We need to check for cases like 1.00000e-10 (yes, this is
+    // disgusting).
+    char* exponent = end - 1;
+    for ( ; ; --exponent) {
+      if (*exponent == 'e') {
+        break;
       }
     }
-    if (*nump != '\0') {
-      *bufp++ = '.';
-      while (*nump != '\0') {
-        *bufp++ = *nump++;
+    char* zerosBeforeExponent = exponent - 1;
+    for ( ; zerosBeforeExponent != decimalPoint; --zerosBeforeExponent) {
+      if (*zerosBeforeExponent != '0') {
+        break;
       }
     }
-    *bufp++ = '\0';
-  }
-  else if (decpt < 0) {
-    *bufp++ = '0';
-    *bufp++ = '.';
-    while (decpt++) {
-      *bufp++ = '0';
+    if (zerosBeforeExponent == decimalPoint) {
+      --zerosBeforeExponent;
     }
+    // Slide the exponent to the left over the trailing zeros.  Don't
+    // worry about copying the trailing NUL character.
+    size_t exponentSize = end - exponent;
+    memmove(zerosBeforeExponent + 1, exponent, exponentSize);
+    length -= exponent - (zerosBeforeExponent + 1);
+  } else {
+    char* trailingZeros = end - 1;
+    for ( ; trailingZeros != decimalPoint; --trailingZeros) {
+      if (*trailingZeros != '0') {
+        break;
+      }
+    }
+    if (trailingZeros == decimalPoint) {
+      --trailingZeros;
+    }
+    length -= end - (trailingZeros + 1);
+  }
 
-    while (*nump != '\0') {
-      *bufp++ = *nump++;
-    }
-    *bufp++ = '\0';
-  }
+  return length;
 }
 #endif /* CharT_is_PRUnichar */
 
 void
-nsTSubstring_CharT::DoAppendFloat( double aFloat, int digits )
+nsTSubstring_CharT::AppendFloat( float aFloat )
 {
   char buf[40];
-  // Use Modified_cnvtf, which is locale-insensitive, instead of the
-  // locale-sensitive PR_snprintf or sprintf(3)
-  Modified_cnvtf(buf, digits, aFloat);
-  AppendASCII(buf);
+  int length = FormatWithoutTrailingZeros(buf, aFloat, 6);
+  AppendASCII(buf, length);
+}
+
+void
+nsTSubstring_CharT::AppendFloat( double aFloat )
+{
+  char buf[40];
+  int length = FormatWithoutTrailingZeros(buf, aFloat, 15);
+  AppendASCII(buf, length);
 }
 
 size_t