Harmony: implement Math.fround.

R=jarin@chromium.org
BUG=v8:2938
LOG=N

Review URL: https://codereview.chromium.org/169513002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19433 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/harmony-math.js

@@ -109,19 +109,19 @@ function MathAtanh(x) {
 }
 
 
-//ES6 draft 09-27-13, section 20.2.2.21.
+// ES6 draft 09-27-13, section 20.2.2.21.
 function MathLog10(x) {
   return MathLog(x) * 0.434294481903251828;  // log10(x) = log(x)/log(10).
 }
 
 
-//ES6 draft 09-27-13, section 20.2.2.22.
+// ES6 draft 09-27-13, section 20.2.2.22.
 function MathLog2(x) {
   return MathLog(x) * 1.442695040888963407;  // log2(x) = log(x)/log(2).
 }
 
 
-//ES6 draft 09-27-13, section 20.2.2.17.
+// ES6 draft 09-27-13, section 20.2.2.17.
 function MathHypot(x, y) {  // Function length is 2.
   // We may want to introduce fast paths for two arguments and when
   // normalization to avoid overflow is not necessary.  For now, we
@@ -154,6 +154,12 @@ function MathHypot(x, y) {  // Function length is 2.
 }
 
 
+// ES6 draft 09-27-13, section 20.2.2.16.
+function MathFround(x) {
+  return %Math_fround(TO_NUMBER_INLINE(x));
+}
+
+
 function ExtendMath() {
   %CheckIsBootstrapping();
 
@@ -169,7 +175,8 @@ function ExtendMath() {
     "atanh", MathAtanh,
     "log10", MathLog10,
     "log2", MathLog2,
-    "hypot", MathHypot
+    "hypot", MathHypot,
+    "fround", MathFround
   ));
 }
 

src/runtime.cc

@@ -7829,6 +7829,16 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_sqrt) {
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_Math_fround) {
+  SealHandleScope shs(isolate);
+  ASSERT(args.length() == 1);
+
+  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
+  float xf = static_cast<float>(x);
+  return isolate->heap()->AllocateHeapNumber(xf);
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_DateMakeDay) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 2);

src/runtime.h

@@ -185,6 +185,7 @@ namespace internal {
   F(Math_pow_cfunction, 2, 1) \
   F(RoundNumber, 1, 1) \
   F(Math_sqrt, 1, 1) \
+  F(Math_fround, 1, 1) \
   \
   /* Regular expressions */ \
   F(RegExpCompile, 3, 1) \

test/mjsunit/harmony/math-fround.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-maths
+
+// Monkey-patch Float32Array.
+Float32Array = function(x) { this[0] = 0; };
+
+assertTrue(isNaN(Math.fround(NaN)));
+assertTrue(isNaN(Math.fround(function() {})));
+assertTrue(isNaN(Math.fround({ toString: function() { return NaN; } })));
+assertTrue(isNaN(Math.fround({ valueOf: function() { return "abc"; } })));
+assertEquals("Infinity", String(1/Math.fround(0)));
+assertEquals("-Infinity", String(1/Math.fround(-0)));
+assertEquals("Infinity", String(Math.fround(Infinity)));
+assertEquals("-Infinity", String(Math.fround(-Infinity)));
+
+assertEquals("Infinity", String(Math.fround(1E200)));
+assertEquals("-Infinity", String(Math.fround(-1E200)));
+assertEquals("Infinity", String(1/Math.fround(1E-300)));
+assertEquals("-Infinity", String(1/Math.fround(-1E-300)));
+
+mantissa_23_shift = Math.pow(2, -23);
+mantissa_29_shift = Math.pow(2, -23-29);
+
+// Javascript implementation of IEEE 754 to test double to single conversion.
+function ieee754float(sign_bit,
+                      exponent_bits,
+                      mantissa_23_bits,
+                      mantissa_29_bits) {
+  this.sign_bit = sign_bit & 1;
+  this.exponent_bits = exponent_bits & ((1 << 11) - 1);
+  this.mantissa_23_bits = mantissa_23_bits & ((1 << 23) - 1);
+  this.mantissa_29_bits = mantissa_29_bits & ((1 << 29) - 1);
+}
+
+ieee754float.prototype.returnSpecial = function() {
+  if (mantissa_23_bits == 0 && mantissa_29_bits == 0) return sign * Infinity;
+  return NaN;
+}
+
+ieee754float.prototype.toDouble = function() {
+  var sign = this.sign_bit ? -1 : 1;
+  var exponent = this.exponent_bits - 1023;
+  if (exponent == -1023) returnSpecial();
+  var mantissa = 1 + this.mantissa_23_bits * mantissa_23_shift +
+                     this.mantissa_29_bits * mantissa_29_shift;
+  return sign * Math.pow(2, exponent) * mantissa;
+}
+
+ieee754float.prototype.toSingle = function() {
+  var sign = this.sign_bit ? -1 : 1;
+  var exponent = this.exponent_bits - 1023;
+  if (exponent == -1023) returnSpecial();
+  if (exponent > 127) return sign * Infinity;
+  if (exponent < -126) return this.toSingleSubnormal(sign, exponent);
+  var round = this.mantissa_29_bits >> 28;
+  var mantissa = 1 + (this.mantissa_23_bits + round) * mantissa_23_shift;
+  return sign * Math.pow(2, exponent) * mantissa;
+}
+
+ieee754float.prototype.toSingleSubnormal = function(sign, exponent) {
+  var shift = -126 - exponent;
+  if (shift > 24) return sign * 0;
+  var round_mask = 1 << (shift - 1);
+  var mantissa_23_bits = this.mantissa_23_bits + (1 << 23);
+  var round = ((mantissa_23_bits & round_mask) != 0) | 0;
+  if (round) {  // Round to even if tied.
+    var tied_mask = round_mask - 1;
+    var result_last_bit_mask = 1 << shift;
+    var tied = this.mantissa_29_bits == 0 &&
+               (mantissa_23_bits & tied_mask ) == 0;
+    var result_already_even = (mantissa_23_bits & result_last_bit_mask) == 0;
+    if (tied && result_already_even) round = 0;
+  }
+  mantissa_23_bits >>= shift;
+  var mantissa = (mantissa_23_bits + round) * mantissa_23_shift;
+  return sign * Math.pow(2, -126) * mantissa;
+}
+
+
+var pi = new ieee754float(0, 0x400, 0x490fda, 0x14442d18);
+assertEquals(pi.toSingle(), Math.fround(pi.toDouble()));
+
+function fuzz_mantissa(sign, exp, m1inc, m2inc) {
+  for (var m1 = 0; m1 < (1 << 23); m1 += m1inc) {
+    for (var m2 = 0; m2 < (1 << 29); m2 += m2inc) {
+      var float = new ieee754float(sign, exp, m1, m2);
+      assertEquals(float.toSingle(), Math.fround(float.toDouble()));
+    }
+  }
+}
+
+for (var sign = 0; sign < 2; sign++) {
+  for (var exp = 1024 - 170; exp < 1024 + 170; exp++) {
+    fuzz_mantissa(sign, exp, 1337 * exp - sign, 127913 * exp - sign);
+  }
+}