Reviewed by Darin.

        - fixed "toPrecision sometimes messes up the last digit on intel Macs"
        http://bugzilla.opendarwin.org/show_bug.cgi?id=7748

        * kjs/number_object.cpp:
        (intPow10): Compute integer powers of 10 using exponentiation by squaring.
        (NumberProtoFunc::callAsFunction): Use intPow10(n) in place of all pow(10.0, n),
        plus a bit of refactoring.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@13676 268f45cc-cd09-0410-ab3c-d52691b4dbfc

diff --git a/JavaScriptCore/ChangeLog b/JavaScriptCore/ChangeLog
index b166258a367c8a2b069d9b98d1d319336384656a..d97ebae9c71e5ee3560aa9babfbc275d6042e94b 100644 (file)
--- a/JavaScriptCore/ChangeLog
+++ b/JavaScriptCore/ChangeLog
@@ -1,3 +1,15 @@
+2006-03-12  Maciej Stachowiak  <mjs@apple.com>
+
+        Reviewed by Darin.
+        
+        - fixed "toPrecision sometimes messes up the last digit on intel Macs"
+        http://bugzilla.opendarwin.org/show_bug.cgi?id=7748
+
+        * kjs/number_object.cpp:
+        (intPow10): Compute integer powers of 10 using exponentiation by squaring.
+        (NumberProtoFunc::callAsFunction): Use intPow10(n) in place of all pow(10.0, n),
+        plus a bit of refactoring.
+
 2006-04-03  Darin Adler  <darin@apple.com>
 
         - tweak config.h and Platform.h to try to get buildbot working

diff --git a/JavaScriptCore/kjs/number_object.cpp b/JavaScriptCore/kjs/number_object.cpp
index de57c5623a5103d83417ff9fb4a302f275e52fc7..cd039580998ae8f9720e37cc9cba4ab11872daa5 100644 (file)
--- a/JavaScriptCore/kjs/number_object.cpp
+++ b/JavaScriptCore/kjs/number_object.cpp
@@ -116,6 +116,38 @@ static UString char_sequence(char c, int count)
     return UString(buf);
 }
 
+static double intPow10(int e)
+{
+  // This function uses the "exponentiation by squaring" algorithm and
+  // long double to quickly and precisely calculate integer powers of 10.0.
+
+  // This is a handy workaround for <rdar://problem/4494756>
+
+  if (e == 0)
+    return 1.0;
+
+  bool negative = e < 0;
+  unsigned exp = negative ? -e : e;
+
+  long double result = 10.0;
+  bool foundOne = false;
+  for (int bit = 31; bit >= 0; bit--) {
+    if (!foundOne) {
+      if ((exp >> bit) & 1)
+        foundOne = true;
+    } else {
+      result = result * result;
+      if ((exp >> bit) & 1)
+        result = result * 10.0;
+    }
+  }
+
+  if (negative)
+    return 1.0 / result;
+  else
+    return result;
+}
+
 // ECMA 15.7.4.2 - 15.7.4.7
 JSValue *NumberProtoFunc::callAsFunction(ExecState *exec, JSObject *thisObj, const List &args)
 {
@@ -238,7 +270,7 @@ JSValue *NumberProtoFunc::callAsFunction(ExecState *exec, JSObject *thisObj, con
       if (!fractionDigits->isUndefined()) {
           double logx = floor(log10(x));
           x /= pow(10.0, logx);
-          double fx = floor(x * pow(10.0, f)) / pow(10.0,f);
+          double fx = floor(x * pow(10.0, f)) / pow(10.0, f);
           double cx = ceil(x * pow(10.0, f)) / pow(10.0, f);
           
           if (fabs(fx-x) < fabs(cx-x))
@@ -333,17 +365,19 @@ JSValue *NumberProtoFunc::callAsFunction(ExecState *exec, JSObject *thisObj, con
       int p = (int)dp;
       
       if (x != 0) {
-          e = static_cast<int>(log10(x));
-          double n = floor(x / pow(10.0, e - p + 1));
-          if (n < pow(10.0, p - 1)) {
+          e = static_cast<int>(trunc(log10(x)));
+          double tens = intPow10(e - p + 1);
+          double n = floor(x / tens);
+          if (n < intPow10(p - 1)) {
               e = e - 1;
-              n = floor(x / pow(10.0, e - p + 1));
+              tens = intPow10(e - p + 1);
+              n = floor(x / tens);
           }
           
-          if (fabs((n + 1) * pow(10.0, e - p + 1) - x) < fabs(n * pow(10.0, e - p + 1) - x))
-              n++;
-          assert(pow(10.0, p - 1) <= n);
-          assert(n < pow(10.0, p));
+          if (fabs((n + 1.0) * tens - x) <= fabs(n * tens - x))
+            ++n;
+          assert(intPow10(p - 1) <= n);
+          assert(n < intPow10(p));
           
           m = integer_part_noexp(n);
           if (e < -6 || e >= p) {