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Fix DoubleToFloat32 corner case

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For a few double value above the max float, we have to round down
to that max float rather than rounding up to infinity.

Bug: chromium:956564
Change-Id: I34be1def5330bd4c3352b792d20dd500f108d9e1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1585852
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61052}
This commit is contained in:
Jakob Kummerow 2019-04-26 17:36:09 +02:00 committed by Commit Bot
parent 4153feb298
commit 7265ea973c
1 changed files with 18 additions and 3 deletions
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21
src/conversions-inl.h
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@ -59,9 +59,24 @@ inline unsigned int FastD2UI(double x) {
inline float DoubleToFloat32(double x) {
typedef std::numeric_limits<float> limits;
if (x > limits::max()) return limits::infinity();
if (x < limits::lowest()) return -limits::infinity();
using limits = std::numeric_limits<float>;
if (x > limits::max()) {
// kRoundingThreshold is the maximum double that rounds down to
// the maximum representable float. Its mantissa bits are:
// 1111111111111111111111101111111111111111111111111111
// [<--- float range --->]
// Note the zero-bit right after the float mantissa range, which
// determines the rounding-down.
static const double kRoundingThreshold = 3.4028235677973362e+38;
if (x <= kRoundingThreshold) return limits::max();
return limits::infinity();
}
if (x < limits::lowest()) {
// Same as above, mirrored to negative numbers.
static const double kRoundingThreshold = -3.4028235677973362e+38;
if (x >= kRoundingThreshold) return limits::lowest();
return -limits::infinity();
}
return static_cast<float>(x);
}