skia2/include/core/SkMath.h

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkMath_DEFINED
#define SkMath_DEFINED

#include "include/core/SkTypes.h"

// 64bit -> 32bit utilities

// Handy util that can be passed two ints, and will automatically promote to
// 64bits before the multiply, so the caller doesn't have to remember to cast
// e.g. (int64_t)a * b;
static inline int64_t sk_64_mul(int64_t a, int64_t b) {
    return a * b;
}

///////////////////////////////////////////////////////////////////////////////

/**
 *  Returns true if value is a power of 2. Does not explicitly check for
 *  value <= 0.
 */
template <typename T> constexpr inline bool SkIsPow2(T value) {
    return (value & (value - 1)) == 0;
}

///////////////////////////////////////////////////////////////////////////////

/**
 *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
 *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
 */
static inline unsigned SkMul16ShiftRound(U16CPU a, U16CPU b, int shift) {
    SkASSERT(a <= 32767);
    SkASSERT(b <= 32767);
    SkASSERT(shift > 0 && shift <= 8);
    unsigned prod = a*b + (1 << (shift - 1));
    return (prod + (prod >> shift)) >> shift;
}

/**
 *  Return a*b/255, rounding any fractional bits.
 *  Only valid if a and b are unsigned and <= 32767.
 */
static inline U8CPU SkMulDiv255Round(U16CPU a, U16CPU b) {
    return SkMul16ShiftRound(a,b,8);
}

#endif