/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkMathPriv_DEFINED
#define SkMathPriv_DEFINED

#include "include/private/SkAssert.h"
#include "include/private/SkCPUTypes.h"
#include "include/private/SkTemplates.h"

#include <bit>
#include <cstddef>
#include <cstdint>

/**
 * Return the number of leading zero bits.
 */
static constexpr int SkCLZ(uint32_t x) {
    return std::countl_zero<uint32_t>(x);
}

/**
 * Return the number of trailing zero bits.
 */
static constexpr int SkCTZ(uint32_t x) {
    return std::countr_zero<uint32_t>(x);
}

/*
 * Return the number of set bits (i.e., the population count) in the provided uint32_t.
 */
static constexpr int SkPopCount(uint32_t x) {
    return std::popcount<uint32_t>(x);
}

/**
 *  Return the integer square root of value, with a bias of bitBias
 */
int32_t SkSqrtBits(int32_t value, int bitBias);

/** Return the integer square root of n, treated as a SkFixed (16.16)
 */
static inline int32_t SkSqrt32(int32_t n) { return SkSqrtBits(n, 15); }

/**
 *  Returns (value < 0 ? 0 : value) efficiently (i.e. no compares or branches)
 */
static inline int SkClampPos(int value) {
    return value & ~(value >> 31);
}

/**
 * Stores numer/denom and numer%denom into div and mod respectively.
 */
template <typename In, typename Out>
inline void SkTDivMod(In numer, In denom, Out* div, Out* mod) {
    *div = static_cast<Out>(numer/denom);
    *mod = static_cast<Out>(numer%denom);
}

/** Returns -1 if n < 0, else returns 0
 */
#define SkExtractSign(n)    ((int32_t)(n) >> 31)

/** If sign == -1, returns -n, else sign must be 0, and returns n.
 Typically used in conjunction with SkExtractSign().
 */
static inline int32_t SkApplySign(int32_t n, int32_t sign) {
    SkASSERT(sign == 0 || sign == -1);
    return (n ^ sign) - sign;
}

/** Return x with the sign of y */
static inline int32_t SkCopySign32(int32_t x, int32_t y) {
    return SkApplySign(x, SkExtractSign(x ^ y));
}

/** Given a positive value and a positive max, return the value
 pinned against max.
 Note: only works as long as max - value doesn't wrap around
 @return max if value >= max, else value
 */
static inline unsigned SkClampUMax(unsigned value, unsigned max) {
    if (value > max) {
        value = max;
    }
    return value;
}

// If a signed int holds min_int (e.g. 0x80000000) it is undefined what happens when
// we negate it (even though we *know* we're 2's complement and we'll get the same
// value back). So we create this helper function that casts to size_t (unsigned) first,
// to avoid the complaint.
static inline size_t sk_negate_to_size_t(int32_t value) {
#if defined(_MSC_VER)
#pragma warning(push)
#pragma warning(disable : 4146)  // Thanks MSVC, we know what we're negating an unsigned
#endif
    return -static_cast<size_t>(value);
#if defined(_MSC_VER)
#pragma warning(pop)
#endif
}

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

/** Return a*b/255, truncating away any fractional bits. Only valid if both
 a and b are 0..255
 */
static inline U8CPU SkMulDiv255Trunc(U8CPU a, U8CPU b) {
    SkASSERT((uint8_t)a == a);
    SkASSERT((uint8_t)b == b);
    unsigned prod = a*b + 1;
    return (prod + (prod >> 8)) >> 8;
}

/** Return (a*b)/255, taking the ceiling of any fractional bits. Only valid if
 both a and b are 0..255. The expected result equals (a * b + 254) / 255.
 */
static inline U8CPU SkMulDiv255Ceiling(U8CPU a, U8CPU b) {
    SkASSERT((uint8_t)a == a);
    SkASSERT((uint8_t)b == b);
    unsigned prod = a*b + 255;
    return (prod + (prod >> 8)) >> 8;
}

/** Just the rounding step in SkDiv255Round: round(value / 255)
 */
static inline unsigned SkDiv255Round(unsigned prod) {
    prod += 128;
    return (prod + (prod >> 8)) >> 8;
}

/**
 * Swap byte order of a 4-byte value, e.g. 0xaarrggbb -> 0xbbggrraa.
 */
#if defined(_MSC_VER)
    #include <stdlib.h>
    static inline uint32_t SkBSwap32(uint32_t v) { return _byteswap_ulong(v); }
#else
    static inline uint32_t SkBSwap32(uint32_t v) { return __builtin_bswap32(v); }
#endif

/**
 *  Returns the log2 of the specified value, were that value to be rounded up
 *  to the next power of 2. It is undefined to pass 0. Examples:
 *  SkNextLog2(1) -> 0
 *  SkNextLog2(2) -> 1
 *  SkNextLog2(3) -> 2
 *  SkNextLog2(4) -> 2
 *  SkNextLog2(5) -> 3
 */
static constexpr int SkNextLog2(uint32_t value) {
    SkASSERT(value != 0);
    return 32 - SkCLZ(value - 1);
}

/**
*  Returns the log2 of the specified value, were that value to be rounded down
*  to the previous power of 2. It is undefined to pass 0. Examples:
*  SkPrevLog2(1) -> 0
*  SkPrevLog2(2) -> 1
*  SkPrevLog2(3) -> 1
*  SkPrevLog2(4) -> 2
*  SkPrevLog2(5) -> 2
*/
static constexpr int SkPrevLog2(uint32_t value) {
    SkASSERT(value != 0);
    return 32 - SkCLZ(value >> 1);
}

/**
 *  Returns the smallest power-of-2 that is >= the specified value. If value
 *  is already a power of 2, then it is returned unchanged. It is undefined
 *  if value is <= 0.
 */
static constexpr int SkNextPow2(int value) {
    SkASSERT(value > 0);
    return 1 << SkNextLog2(static_cast<uint32_t>(value));
}

/**
*  Returns the largest power-of-2 that is <= the specified value. If value
*  is already a power of 2, then it is returned unchanged. It is undefined
*  if value is <= 0.
*/
static constexpr int SkPrevPow2(int value) {
    SkASSERT(value > 0);
    return 1 << SkPrevLog2(static_cast<uint32_t>(value));
}

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

/**
 * Returns the next power of 2 >= n or n if the next power of 2 can't be represented by size_t.
 */
static constexpr size_t SkNextSizePow2(size_t n) {
    constexpr int kNumSizeTBits = 8 * sizeof(size_t);
    constexpr size_t kHighBitSet = size_t(1) << (kNumSizeTBits - 1);

    if (!n) {
        return 1;
    } else if (n >= kHighBitSet) {
        return n;
    }

    n--;
    uint32_t shift = 1;
    while (shift < kNumSizeTBits) {
        n |= n >> shift;
        shift <<= 1;
    }
    return n + 1;
}

// conservative check. will return false for very large values that "could" fit
template <typename T> static inline bool SkFitsInFixed(T x) {
    return SkTAbs(x) <= 32767.0f;
}

#endif