You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
123 lines
4.0 KiB
123 lines
4.0 KiB
// Copyright 2017 The Chromium Authors. All rights reserved.
|
|
// Use of this source code is governed by a BSD-style license that can be
|
|
// found in the LICENSE file.
|
|
|
|
#ifndef BASE_NUMERICS_SAFE_MATH_ARM_IMPL_H_
|
|
#define BASE_NUMERICS_SAFE_MATH_ARM_IMPL_H_
|
|
|
|
#include <cassert>
|
|
#include <limits>
|
|
#include <type_traits>
|
|
|
|
#include "base/numerics/safe_conversions.h"
|
|
|
|
namespace base {
|
|
namespace internal {
|
|
|
|
template <typename T, typename U>
|
|
struct CheckedMulFastAsmOp {
|
|
static const bool is_supported =
|
|
FastIntegerArithmeticPromotion<T, U>::is_contained;
|
|
|
|
// The following is much more efficient than the Clang and GCC builtins for
|
|
// performing overflow-checked multiplication when a twice wider type is
|
|
// available. The below compiles down to 2-3 instructions, depending on the
|
|
// width of the types in use.
|
|
// As an example, an int32_t multiply compiles to:
|
|
// smull r0, r1, r0, r1
|
|
// cmp r1, r1, asr #31
|
|
// And an int16_t multiply compiles to:
|
|
// smulbb r1, r1, r0
|
|
// asr r2, r1, #16
|
|
// cmp r2, r1, asr #15
|
|
template <typename V>
|
|
__attribute__((always_inline)) static bool Do(T x, U y, V* result) {
|
|
using Promotion = typename FastIntegerArithmeticPromotion<T, U>::type;
|
|
Promotion presult;
|
|
|
|
presult = static_cast<Promotion>(x) * static_cast<Promotion>(y);
|
|
*result = static_cast<V>(presult);
|
|
return IsValueInRangeForNumericType<V>(presult);
|
|
}
|
|
};
|
|
|
|
template <typename T, typename U>
|
|
struct ClampedAddFastAsmOp {
|
|
static const bool is_supported =
|
|
BigEnoughPromotion<T, U>::is_contained &&
|
|
IsTypeInRangeForNumericType<
|
|
int32_t,
|
|
typename BigEnoughPromotion<T, U>::type>::value;
|
|
|
|
template <typename V>
|
|
__attribute__((always_inline)) static V Do(T x, U y) {
|
|
// This will get promoted to an int, so let the compiler do whatever is
|
|
// clever and rely on the saturated cast to bounds check.
|
|
if (IsIntegerArithmeticSafe<int, T, U>::value)
|
|
return saturated_cast<V>(x + y);
|
|
|
|
int32_t result;
|
|
int32_t x_i32 = x;
|
|
int32_t y_i32 = y;
|
|
|
|
asm("qadd %[result], %[first], %[second]"
|
|
: [result] "=r"(result)
|
|
: [first] "r"(x_i32), [second] "r"(y_i32));
|
|
return saturated_cast<V>(result);
|
|
}
|
|
};
|
|
|
|
template <typename T, typename U>
|
|
struct ClampedSubFastAsmOp {
|
|
static const bool is_supported =
|
|
BigEnoughPromotion<T, U>::is_contained &&
|
|
IsTypeInRangeForNumericType<
|
|
int32_t,
|
|
typename BigEnoughPromotion<T, U>::type>::value;
|
|
|
|
template <typename V>
|
|
__attribute__((always_inline)) static V Do(T x, U y) {
|
|
// This will get promoted to an int, so let the compiler do whatever is
|
|
// clever and rely on the saturated cast to bounds check.
|
|
if (IsIntegerArithmeticSafe<int, T, U>::value)
|
|
return saturated_cast<V>(x - y);
|
|
|
|
int32_t result;
|
|
int32_t x_i32 = x;
|
|
int32_t y_i32 = y;
|
|
|
|
asm("qsub %[result], %[first], %[second]"
|
|
: [result] "=r"(result)
|
|
: [first] "r"(x_i32), [second] "r"(y_i32));
|
|
return saturated_cast<V>(result);
|
|
}
|
|
};
|
|
|
|
template <typename T, typename U>
|
|
struct ClampedMulFastAsmOp {
|
|
static const bool is_supported = CheckedMulFastAsmOp<T, U>::is_supported;
|
|
|
|
template <typename V>
|
|
__attribute__((always_inline)) static V Do(T x, U y) {
|
|
// Use the CheckedMulFastAsmOp for full-width 32-bit values, because
|
|
// it's fewer instructions than promoting and then saturating.
|
|
if (!IsIntegerArithmeticSafe<int32_t, T, U>::value &&
|
|
!IsIntegerArithmeticSafe<uint32_t, T, U>::value) {
|
|
V result;
|
|
if (CheckedMulFastAsmOp<T, U>::Do(x, y, &result))
|
|
return result;
|
|
return CommonMaxOrMin<V>(IsValueNegative(x) ^ IsValueNegative(y));
|
|
}
|
|
|
|
assert((FastIntegerArithmeticPromotion<T, U>::is_contained));
|
|
using Promotion = typename FastIntegerArithmeticPromotion<T, U>::type;
|
|
return saturated_cast<V>(static_cast<Promotion>(x) *
|
|
static_cast<Promotion>(y));
|
|
}
|
|
};
|
|
|
|
} // namespace internal
|
|
} // namespace base
|
|
|
|
#endif // BASE_NUMERICS_SAFE_MATH_ARM_IMPL_H_
|