Mike Klein | d280d42 | 2016-10-31 09:20:54 -0400 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2016 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 SkFixed15_DEFINED |
| 9 | #define SkFixed15_DEFINED |
| 10 | |
Mike Klein | c0bd9f9 | 2019-04-23 12:05:21 -0500 | [diff] [blame] | 11 | #include "include/core/SkTypes.h" |
Mike Klein | d280d42 | 2016-10-31 09:20:54 -0400 | [diff] [blame] | 12 | |
| 13 | // SkFixed15 is a fixed point value that represents values in [0,1] as [0x0000, 0x8000]. |
| 14 | // This mapping allows us to implement most operations in tightly packed 16-bit SIMD, |
| 15 | // most notably multiplying using Q15 multiplication instructions (and a little fixup). |
| 16 | |
| 17 | class SkFixed15 { |
| 18 | public: |
| 19 | SkFixed15() = default; |
| 20 | |
| 21 | SkFixed15(float val) : fVal(val * 32768) { SkASSERT(0.0f <= val && val <= 1.0f); } |
| 22 | explicit operator float() const { return fVal * (1/32768.0f); } |
| 23 | |
| 24 | static SkFixed15 Load(uint16_t val) { |
| 25 | SkASSERT(val <= 32768); |
| 26 | return val; |
| 27 | } |
| 28 | uint16_t store() const { return fVal; } |
| 29 | |
| 30 | static SkFixed15 FromU8(uint8_t val) { |
| 31 | return val*128 + (val>>1) // 32768/255 == 128.50196..., which is very close to 128 + 0.5. |
| 32 | + ((val+1)>>8); // All val but 255 are correct. +1 if val == 255 to get 32768. |
| 33 | } |
| 34 | |
Mike Klein | d32b817 | 2017-01-17 10:19:50 -0500 | [diff] [blame] | 35 | uint8_t to_u8() const { |
| 36 | // FromU8() and to_u8() roundtrip all bytes. |
| 37 | // There is still much room to tweak this towards the ideal, a rounding scale by 255/32768. |
| 38 | return (fVal - (fVal>>8))>>7; |
| 39 | } |
| 40 | |
Mike Klein | d280d42 | 2016-10-31 09:20:54 -0400 | [diff] [blame] | 41 | SkFixed15 operator +(SkFixed15 o) const { return fVal + o.fVal; } |
| 42 | SkFixed15 operator -(SkFixed15 o) const { return fVal - o.fVal; } |
| 43 | SkFixed15 operator *(SkFixed15 o) const { return (fVal * o.fVal + (1<<14)) >> 15; } |
| 44 | SkFixed15 operator<<(int bits) const { return fVal << bits; } |
| 45 | SkFixed15 operator>>(int bits) const { return fVal >> bits; } |
| 46 | |
| 47 | SkFixed15& operator +=(SkFixed15 o) { return (*this = *this + o); } |
| 48 | SkFixed15& operator -=(SkFixed15 o) { return (*this = *this - o); } |
| 49 | SkFixed15& operator *=(SkFixed15 o) { return (*this = *this * o); } |
| 50 | SkFixed15& operator<<=(int bits) { return (*this = *this << bits); } |
| 51 | SkFixed15& operator>>=(int bits) { return (*this = *this >> bits); } |
| 52 | |
| 53 | bool operator==(SkFixed15 o) const { return fVal == o.fVal; } |
| 54 | bool operator!=(SkFixed15 o) const { return fVal != o.fVal; } |
| 55 | bool operator<=(SkFixed15 o) const { return fVal <= o.fVal; } |
| 56 | bool operator>=(SkFixed15 o) const { return fVal >= o.fVal; } |
| 57 | bool operator< (SkFixed15 o) const { return fVal < o.fVal; } |
| 58 | bool operator> (SkFixed15 o) const { return fVal > o.fVal; } |
| 59 | |
| 60 | private: |
| 61 | SkFixed15(int val) : fVal(val) {} |
| 62 | |
| 63 | uint16_t fVal; |
| 64 | }; |
| 65 | |
| 66 | // Notes |
| 67 | // - SSSE3+ multiply is _mm_abs_epi16(_mm_mulhrs_epi16(x, y)); |
| 68 | // - NEON multipy is vsraq_n_u16(vabsq_s16(vqrdmulhq_s16(x,y)), |
| 69 | // vandq_s16(x,y), 15); |
| 70 | // - Conversion to and from float can be done manually with bit masks and float add/subtract, |
| 71 | // rather than the naive version here involving int<->float conversion and float multiply. |
Mike Klein | cd5e7d7 | 2016-10-31 10:08:55 -0400 | [diff] [blame] | 72 | // - On x86, conversion to float is _mm_sub_ps(_mm_unpacklo_epi16(x, _mm_set1_epi16(0x4380)), |
| 73 | // _mm_set1_ps(256.0f)). // 0x43800000 |
| 74 | // - On ARM, we can use the vcvtq_n_f32_u32(vmovl_u16(x), 15) to convert to float, |
| 75 | // and vcvtq_n_u32_f32(..., 15) for the other way around. |
Mike Klein | d280d42 | 2016-10-31 09:20:54 -0400 | [diff] [blame] | 76 | |
| 77 | #endif//SkFixed15_DEFINED |