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swiftshader
Commit e1051cba by Nicolas Capens Committed by Nicolas Capens
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Fix undefined behavior in minifloat conversion

Shifting a 32-bit value by 32 or more is undefined behavior in C++. This previously happened in this code when converting a 32-bit float value to an 11- or 10-bit minifloat which is too small to be represented as a denormal, and should produce 0 instead. Instead of going through this arithmetic for denormals, just test whether the input value is too small to produce a valid denormal, and return 0 instead. Bug: chromium:1117433 Change-Id: I8149996fb6d66d328db45725c4cdb81dc7826a10 Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/48069 Presubmit-Ready: Nicolas Capens <nicolascapens@google.com> Tested-by: 's avatarNicolas Capens <nicolascapens@google.com> Kokoro-Result: kokoro <noreply+kokoro@google.com> Reviewed-by: 's avatarAlexis Hétu <sugoi@google.com>
parent 558540fe
Showing with 16 additions and 4 deletions
src/System/Half.hpp
......@@ -174,7 +174,8 @@ public:
const unsigned int float11ExponentBias = 14;
const unsigned int float32Maxfloat11 = 0x477E0000;
const unsigned int float32Minfloat11 = 0x38800000;
const unsigned int float32MinNormfloat11 = 0x38800000;
const unsigned int float32MinDenormfloat11 = 0x35000080;
const unsigned int float32Bits = *reinterpret_cast<unsigned int *>(&fp32);
const bool float32Sign = (float32Bits & float32SignMask) == float32SignMask;
......@@ -210,9 +211,14 @@ public:
// The number is too large to be represented as a float11, set to max
return float11Max;
}
else if(float32Val < float32MinDenormfloat11)
{
// The number is too small to be represented as a denormalized float11, set to 0
return 0;
}
else
{
if(float32Val < float32Minfloat11)
if(float32Val < float32MinNormfloat11)
{
// The number is too small to be represented as a normalized float11
// Convert it to a denormalized value.
......@@ -247,7 +253,8 @@ public:
const unsigned int float10ExponentBias = 14;
const unsigned int float32Maxfloat10 = 0x477C0000;
const unsigned int float32Minfloat10 = 0x38800000;
const unsigned int float32MinNormfloat10 = 0x38800000;
const unsigned int float32MinDenormfloat10 = 0x35800040;
const unsigned int float32Bits = *reinterpret_cast<unsigned int *>(&fp32);
const bool float32Sign = (float32Bits & float32SignMask) == float32SignMask;
......@@ -283,9 +290,14 @@ public:
// The number is too large to be represented as a float10, set to max
return float10Max;
}
else if(float32Val < float32MinDenormfloat10)
{
// The number is too small to be represented as a denormalized float10, set to 0
return 0;
}
else
{
if(float32Val < float32Minfloat10)
if(float32Val < float32MinNormfloat10)
{
// The number is too small to be represented as a normalized float10
// Convert it to a denormalized value.
......
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