sky/engine/wtf/SaturatedArithmetic.h

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#ifndef SKY_ENGINE_WTF_SATURATEDARITHMETIC_H_
#define SKY_ENGINE_WTF_SATURATEDARITHMETIC_H_

#include <stdint.h>
#include <limits>
#include "sky/engine/wtf/CPU.h"

#if CPU(ARM) && COMPILER(GCC) && __OPTIMIZE__

// If we're building ARM on GCC we replace the C++ versions with some
// native ARM assembly for speed.
#include "sky/engine/wtf/asm/SaturatedArithmeticARM.h"

#else

ALWAYS_INLINE int32_t saturatedAddition(int32_t a, int32_t b)
{
    uint32_t ua = a;
    uint32_t ub = b;
    uint32_t result = ua + ub;

    // Can only overflow if the signed bit of the two values match. If the
    // signed bit of the result and one of the values differ it overflowed.

    if (~(ua ^ ub) & (result ^ ua) & (1 << 31))
        return std::numeric_limits<int>::max() + (ua >> 31);

    return result;
}

ALWAYS_INLINE int32_t saturatedSubtraction(int32_t a, int32_t b)
{
    uint32_t ua = a;
    uint32_t ub = b;
    uint32_t result = ua - ub;

    // Can only overflow if the signed bit of the two input values differ. If
    // the signed bit of the result and the first value differ it overflowed.

    if ((ua ^ ub) & (result ^ ua) & (1 << 31))
        return std::numeric_limits<int>::max() + (ua >> 31);

    return result;
}

inline int getMaxSaturatedSetResultForTesting(int FractionalShift)
{
    // For C version the set function maxes out to max int, this differs from
    // the ARM asm version, see SaturatedArithmetiARM.h for the equivalent asm
    // version.
    return std::numeric_limits<int>::max();
}

inline int getMinSaturatedSetResultForTesting(int FractionalShift)
{
    return std::numeric_limits<int>::min();
}

ALWAYS_INLINE int saturatedSet(int value, int FractionalShift)
{
    const int intMaxForLayoutUnit =
        std::numeric_limits<int>::max() >> FractionalShift;

    const int intMinForLayoutUnit =
        std::numeric_limits<int>::min() >> FractionalShift;

    if (value > intMaxForLayoutUnit)
        return std::numeric_limits<int>::max();

    if (value < intMinForLayoutUnit)
        return std::numeric_limits<int>::min();

    return value << FractionalShift;
}


ALWAYS_INLINE int saturatedSet(unsigned value, int FractionalShift)
{
    const unsigned intMaxForLayoutUnit =
        std::numeric_limits<int>::max() >> FractionalShift;

    if (value >= intMaxForLayoutUnit)
        return std::numeric_limits<int>::max();

    return value << FractionalShift;
}

#endif // CPU(ARM) && COMPILER(GCC)
#endif  // SKY_ENGINE_WTF_SATURATEDARITHMETIC_H_