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      1 
      2 /*
      3  * Copyright 2006 The Android Open Source Project
      4  *
      5  * Use of this source code is governed by a BSD-style license that can be
      6  * found in the LICENSE file.
      7  */
      8 
      9 
     10 #ifndef SkMath_DEFINED
     11 #define SkMath_DEFINED
     12 
     13 #include "SkTypes.h"
     14 
     15 // 64bit -> 32bit utilities
     16 
     17 /**
     18  *  Return true iff the 64bit value can exactly be represented in signed 32bits
     19  */
     20 static inline bool sk_64_isS32(int64_t value) {
     21     return (int32_t)value == value;
     22 }
     23 
     24 /**
     25  *  Return the 64bit argument as signed 32bits, asserting in debug that the arg
     26  *  exactly fits in signed 32bits. In the release build, no checks are preformed
     27  *  and the return value if the arg does not fit is undefined.
     28  */
     29 static inline int32_t sk_64_asS32(int64_t value) {
     30     SkASSERT(sk_64_isS32(value));
     31     return (int32_t)value;
     32 }
     33 
     34 // Handy util that can be passed two ints, and will automatically promote to
     35 // 64bits before the multiply, so the caller doesn't have to remember to cast
     36 // e.g. (int64_t)a * b;
     37 static inline int64_t sk_64_mul(int64_t a, int64_t b) {
     38     return a * b;
     39 }
     40 
     41 ///////////////////////////////////////////////////////////////////////////////
     42 
     43 /**
     44  *  Computes numer1 * numer2 / denom in full 64 intermediate precision.
     45  *  It is an error for denom to be 0. There is no special handling if
     46  *  the result overflows 32bits.
     47  */
     48 static inline int32_t SkMulDiv(int32_t numer1, int32_t numer2, int32_t denom) {
     49     SkASSERT(denom);
     50 
     51     int64_t tmp = sk_64_mul(numer1, numer2) / denom;
     52     return sk_64_asS32(tmp);
     53 }
     54 
     55 /**
     56  *  Return the integer square root of value, with a bias of bitBias
     57  */
     58 int32_t SkSqrtBits(int32_t value, int bitBias);
     59 
     60 /** Return the integer square root of n, treated as a SkFixed (16.16)
     61  */
     62 #define SkSqrt32(n)         SkSqrtBits(n, 15)
     63 
     64 /**
     65  *  Returns (value < 0 ? 0 : value) efficiently (i.e. no compares or branches)
     66  */
     67 static inline int SkClampPos(int value) {
     68     return value & ~(value >> 31);
     69 }
     70 
     71 /** Given an integer and a positive (max) integer, return the value
     72  *  pinned against 0 and max, inclusive.
     73  *  @param value    The value we want returned pinned between [0...max]
     74  *  @param max      The positive max value
     75  *  @return 0 if value < 0, max if value > max, else value
     76  */
     77 static inline int SkClampMax(int value, int max) {
     78     // ensure that max is positive
     79     SkASSERT(max >= 0);
     80     if (value < 0) {
     81         value = 0;
     82     }
     83     if (value > max) {
     84         value = max;
     85     }
     86     return value;
     87 }
     88 
     89 /**
     90  *  Returns true if value is a power of 2. Does not explicitly check for
     91  *  value <= 0.
     92  */
     93 template <typename T> constexpr inline bool SkIsPow2(T value) {
     94     return (value & (value - 1)) == 0;
     95 }
     96 
     97 ///////////////////////////////////////////////////////////////////////////////
     98 
     99 /**
    100  *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
    101  *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
    102  */
    103 static inline unsigned SkMul16ShiftRound(U16CPU a, U16CPU b, int shift) {
    104     SkASSERT(a <= 32767);
    105     SkASSERT(b <= 32767);
    106     SkASSERT(shift > 0 && shift <= 8);
    107     unsigned prod = a*b + (1 << (shift - 1));
    108     return (prod + (prod >> shift)) >> shift;
    109 }
    110 
    111 /**
    112  *  Return a*b/255, rounding any fractional bits.
    113  *  Only valid if a and b are unsigned and <= 32767.
    114  */
    115 static inline U8CPU SkMulDiv255Round(U16CPU a, U16CPU b) {
    116     SkASSERT(a <= 32767);
    117     SkASSERT(b <= 32767);
    118     unsigned prod = a*b + 128;
    119     return (prod + (prod >> 8)) >> 8;
    120 }
    121 
    122 /**
    123  * Stores numer/denom and numer%denom into div and mod respectively.
    124  */
    125 template <typename In, typename Out>
    126 inline void SkTDivMod(In numer, In denom, Out* div, Out* mod) {
    127 #ifdef SK_CPU_ARM32
    128     // If we wrote this as in the else branch, GCC won't fuse the two into one
    129     // divmod call, but rather a div call followed by a divmod.  Silly!  This
    130     // version is just as fast as calling __aeabi_[u]idivmod manually, but with
    131     // prettier code.
    132     //
    133     // This benches as around 2x faster than the code in the else branch.
    134     const In d = numer/denom;
    135     *div = static_cast<Out>(d);
    136     *mod = static_cast<Out>(numer-d*denom);
    137 #else
    138     // On x86 this will just be a single idiv.
    139     *div = static_cast<Out>(numer/denom);
    140     *mod = static_cast<Out>(numer%denom);
    141 #endif
    142 }
    143 
    144 #endif
    145