1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef SaturatedArithmeticARM_h 6 #define SaturatedArithmeticARM_h 7 8 #include "wtf/CPU.h" 9 #include <limits> 10 #include <stdint.h> 11 12 ALWAYS_INLINE int32_t saturatedAddition(int32_t a, int32_t b) 13 { 14 int32_t result; 15 16 asm("qadd %[output],%[first],%[second]" 17 : [output] "=r" (result) 18 : [first] "r" (a), 19 [second] "r" (b)); 20 21 return result; 22 } 23 24 ALWAYS_INLINE int32_t saturatedSubtraction(int32_t a, int32_t b) 25 { 26 int32_t result; 27 28 asm("qsub %[output],%[first],%[second]" 29 : [output] "=r" (result) 30 : [first] "r" (a), 31 [second] "r" (b)); 32 33 return result; 34 } 35 36 inline int getMaxSaturatedSetResultForTesting(int FractionalShift) 37 { 38 // For ARM Asm version the set function maxes out to the biggest 39 // possible integer part with the fractional part zero'd out. 40 // e.g. 0x7fffffc0. 41 return std::numeric_limits<int>::max() & ~((1 << FractionalShift)-1); 42 } 43 44 inline int getMinSaturatedSetResultForTesting(int FractionalShift) 45 { 46 return std::numeric_limits<int>::min(); 47 } 48 49 ALWAYS_INLINE int saturatedSet(int value, int FractionalShift) 50 { 51 // Figure out how many bits are left for storing the integer part of 52 // the fixed point number, and saturate our input to that 53 const int saturate = 32 - FractionalShift; 54 55 int result; 56 57 // The following ARM code will Saturate the passed value to the number of 58 // bits used for the whole part of the fixed point representation, then 59 // shift it up into place. This will result in the low <FractionShift> bits 60 // all being 0's. When the value saturates this gives a different result 61 // to from the C++ case; in the C++ code a saturated value has all the low 62 // bits set to 1 (for a +ve number at least). This cannot be done rapidly 63 // in ARM ... we live with the difference, for the sake of speed. 64 65 asm("ssat %[output],%[saturate],%[value]\n\t" 66 "lsl %[output],%[shift]" 67 : [output] "=r" (result) 68 : [value] "r" (value), 69 [saturate] "n" (saturate), 70 [shift] "n" (FractionalShift)); 71 72 return result; 73 } 74 75 76 ALWAYS_INLINE int saturatedSet(unsigned value, int FractionalShift) 77 { 78 // Here we are being passed an unsigned value to saturate, 79 // even though the result is returned as a signed integer. The ARM 80 // instruction for unsigned saturation therefore needs to be given one 81 // less bit (i.e. the sign bit) for the saturation to work correctly; hence 82 // the '31' below. 83 const int saturate = 31 - FractionalShift; 84 85 // The following ARM code will Saturate the passed value to the number of 86 // bits used for the whole part of the fixed point representation, then 87 // shift it up into place. This will result in the low <FractionShift> bits 88 // all being 0's. When the value saturates this gives a different result 89 // to from the C++ case; in the C++ code a saturated value has all the low 90 // bits set to 1. This cannot be done rapidly in ARM, so we live with the 91 // difference, for the sake of speed. 92 93 int result; 94 95 asm("usat %[output],%[saturate],%[value]\n\t" 96 "lsl %[output],%[shift]" 97 : [output] "=r" (result) 98 : [value] "r" (value), 99 [saturate] "n" (saturate), 100 [shift] "n" (FractionalShift)); 101 102 return result; 103 } 104 105 #endif // SaturatedArithmeticARM_h 106
