SkMath.h revision e16efc1882ab34a0bb3ae361a2d37f840044cf87 
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/**
16 *  Computes numer1 * numer2 / denom in full 64 intermediate precision.
17 *  It is an error for denom to be 0. There is no special handling if
18 *  the result overflows 32bits.
19 */
20int32_t SkMulDiv(int32_t numer1, int32_t numer2, int32_t denom);
21
22/**
23 *  Computes (numer1 << shift) / denom in full 64 intermediate precision.
24 *  It is an error for denom to be 0. There is no special handling if
25 *  the result overflows 32bits.
26 */
27int32_t SkDivBits(int32_t numer, int32_t denom, int shift);
28
29/**
30 *  Return the integer square root of value, with a bias of bitBias
31 */
32int32_t SkSqrtBits(int32_t value, int bitBias);
33
34/** Return the integer square root of n, treated as a SkFixed (16.16)
35 */
36#define SkSqrt32(n)         SkSqrtBits(n, 15)
37
38///////////////////////////////////////////////////////////////////////////////
39
40//! Returns the number of leading zero bits (0...32)
41int SkCLZ_portable(uint32_t);
42
43#if defined(SK_CPU_ARM)
44    #define SkCLZ(x)    __builtin_clz(x)
45#endif
46
47#ifndef SkCLZ
48    #define SkCLZ(x)    SkCLZ_portable(x)
49#endif
50
51/**
52 *  Returns (value < 0 ? 0 : value) efficiently (i.e. no compares or branches)
53 */
54static inline int SkClampPos(int value) {
55    return value & ~(value >> 31);
56}
57
58/** Given an integer and a positive (max) integer, return the value
59 *  pinned against 0 and max, inclusive.
60 *  @param value    The value we want returned pinned between [0...max]
61 *  @param max      The positive max value
62 *  @return 0 if value < 0, max if value > max, else value
63 */
64static inline int SkClampMax(int value, int max) {
65    // ensure that max is positive
66    SkASSERT(max >= 0);
67    if (value < 0) {
68        value = 0;
69    }
70    if (value > max) {
71        value = max;
72    }
73    return value;
74}
75
76/**
77 *  Returns the smallest power-of-2 that is >= the specified value. If value
78 *  is already a power of 2, then it is returned unchanged. It is undefined
79 *  if value is <= 0.
80 */
81static inline int SkNextPow2(int value) {
82    SkASSERT(value > 0);
83    return 1 << (32 - SkCLZ(value - 1));
84}
85
86/**
87 *  Returns the log2 of the specified value, were that value to be rounded up
88 *  to the next power of 2. It is undefined to pass 0. Examples:
89 *  SkNextLog2(1) -> 0
90 *  SkNextLog2(2) -> 1
91 *  SkNextLog2(3) -> 2
92 *  SkNextLog2(4) -> 2
93 *  SkNextLog2(5) -> 3
94 */
95static inline int SkNextLog2(uint32_t value) {
96    SkASSERT(value != 0);
97    return 32 - SkCLZ(value - 1);
98}
99
100/**
101 *  Returns true if value is a power of 2. Does not explicitly check for
102 *  value <= 0.
103 */
104static inline bool SkIsPow2(int value) {
105    return (value & (value - 1)) == 0;
106}
107
108///////////////////////////////////////////////////////////////////////////////
109
110/**
111 *  SkMulS16(a, b) multiplies a * b, but requires that a and b are both int16_t.
112 *  With this requirement, we can generate faster instructions on some
113 *  architectures.
114 */
115#ifdef SK_ARM_HAS_EDSP
116    static inline int32_t SkMulS16(S16CPU x, S16CPU y) {
117        SkASSERT((int16_t)x == x);
118        SkASSERT((int16_t)y == y);
119        int32_t product;
120        asm("smulbb %0, %1, %2 \n"
121            : "=r"(product)
122            : "r"(x), "r"(y)
123            );
124        return product;
125    }
126#else
127    #ifdef SK_DEBUG
128        static inline int32_t SkMulS16(S16CPU x, S16CPU y) {
129            SkASSERT((int16_t)x == x);
130            SkASSERT((int16_t)y == y);
131            return x * y;
132        }
133    #else
134        #define SkMulS16(x, y)  ((x) * (y))
135    #endif
136#endif
137
138/**
139 *  Return a*b/((1 << shift) - 1), rounding any fractional bits.
140 *  Only valid if a and b are unsigned and <= 32767 and shift is > 0 and <= 8
141 */
142static inline unsigned SkMul16ShiftRound(unsigned a, unsigned b, int shift) {
143    SkASSERT(a <= 32767);
144    SkASSERT(b <= 32767);
145    SkASSERT(shift > 0 && shift <= 8);
146    unsigned prod = SkMulS16(a, b) + (1 << (shift - 1));
147    return (prod + (prod >> shift)) >> shift;
148}
149
150/**
151 *  Return a*b/255, rounding any fractional bits. Only valid if both
152 *  a and b are 0..255
153 */
154static inline U8CPU SkMulDiv255Round(U8CPU a, U8CPU b) {
155    SkASSERT((uint8_t)a == a);
156    SkASSERT((uint8_t)b == b);
157    unsigned prod = SkMulS16(a, b) + 128;
158    return (prod + (prod >> 8)) >> 8;
159}
160
161#endif
162