reed@google.com | 4b163ed | 2012-08-07 21:35:13 +0000 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2012 Google Inc. |
| 3 | * |
| 4 | * Use of this source code is governed by a BSD-style license that can be |
| 5 | * found in the LICENSE file. |
| 6 | */ |
| 7 | |
| 8 | #ifndef SkMathPriv_DEFINED |
| 9 | #define SkMathPriv_DEFINED |
| 10 | |
| 11 | #include "SkMath.h" |
| 12 | |
| 13 | /** Returns -1 if n < 0, else returns 0 |
| 14 | */ |
| 15 | #define SkExtractSign(n) ((int32_t)(n) >> 31) |
| 16 | |
| 17 | /** If sign == -1, returns -n, else sign must be 0, and returns n. |
| 18 | Typically used in conjunction with SkExtractSign(). |
| 19 | */ |
| 20 | static inline int32_t SkApplySign(int32_t n, int32_t sign) { |
| 21 | SkASSERT(sign == 0 || sign == -1); |
| 22 | return (n ^ sign) - sign; |
| 23 | } |
| 24 | |
| 25 | /** Return x with the sign of y */ |
| 26 | static inline int32_t SkCopySign32(int32_t x, int32_t y) { |
| 27 | return SkApplySign(x, SkExtractSign(x ^ y)); |
| 28 | } |
| 29 | |
| 30 | /** Given a positive value and a positive max, return the value |
| 31 | pinned against max. |
| 32 | Note: only works as long as max - value doesn't wrap around |
| 33 | @return max if value >= max, else value |
| 34 | */ |
| 35 | static inline unsigned SkClampUMax(unsigned value, unsigned max) { |
| 36 | #ifdef SK_CPU_HAS_CONDITIONAL_INSTR |
| 37 | if (value > max) { |
| 38 | value = max; |
| 39 | } |
| 40 | return value; |
| 41 | #else |
| 42 | int diff = max - value; |
| 43 | // clear diff if diff is positive |
| 44 | diff &= diff >> 31; |
rmistry@google.com | fbfcd56 | 2012-08-23 18:09:54 +0000 | [diff] [blame^] | 45 | |
reed@google.com | 4b163ed | 2012-08-07 21:35:13 +0000 | [diff] [blame] | 46 | return value + diff; |
| 47 | #endif |
| 48 | } |
| 49 | |
| 50 | /** Computes the 64bit product of a * b, and then shifts the answer down by |
| 51 | shift bits, returning the low 32bits. shift must be [0..63] |
| 52 | e.g. to perform a fixedmul, call SkMulShift(a, b, 16) |
| 53 | */ |
| 54 | int32_t SkMulShift(int32_t a, int32_t b, unsigned shift); |
| 55 | |
reed@google.com | 4b163ed | 2012-08-07 21:35:13 +0000 | [diff] [blame] | 56 | /** Return the integer cube root of value, with a bias of bitBias |
| 57 | */ |
| 58 | int32_t SkCubeRootBits(int32_t value, int bitBias); |
| 59 | |
| 60 | /////////////////////////////////////////////////////////////////////////////// |
| 61 | |
| 62 | /** Return a*b/255, truncating away any fractional bits. Only valid if both |
| 63 | a and b are 0..255 |
| 64 | */ |
| 65 | static inline U8CPU SkMulDiv255Trunc(U8CPU a, U8CPU b) { |
| 66 | SkASSERT((uint8_t)a == a); |
| 67 | SkASSERT((uint8_t)b == b); |
| 68 | unsigned prod = SkMulS16(a, b) + 1; |
| 69 | return (prod + (prod >> 8)) >> 8; |
| 70 | } |
| 71 | |
| 72 | /** Return (a*b)/255, taking the ceiling of any fractional bits. Only valid if |
| 73 | both a and b are 0..255. The expected result equals (a * b + 254) / 255. |
| 74 | */ |
| 75 | static inline U8CPU SkMulDiv255Ceiling(U8CPU a, U8CPU b) { |
| 76 | SkASSERT((uint8_t)a == a); |
| 77 | SkASSERT((uint8_t)b == b); |
| 78 | unsigned prod = SkMulS16(a, b) + 255; |
| 79 | return (prod + (prod >> 8)) >> 8; |
| 80 | } |
| 81 | |
| 82 | /** Just the rounding step in SkDiv255Round: round(value / 255) |
| 83 | */ |
| 84 | static inline unsigned SkDiv255Round(unsigned prod) { |
| 85 | prod += 128; |
| 86 | return (prod + (prod >> 8)) >> 8; |
| 87 | } |
| 88 | |
| 89 | #endif |
| 90 | |