| // 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 SAFEMATH_SAFE_MATH_ARM_IMPL_H_ |
| #define SAFEMATH_SAFE_MATH_ARM_IMPL_H_ |
| |
| #include <cassert> |
| #include <limits> |
| #include <type_traits> |
| |
| #include <safemath/safe_conversions.h> |
| |
| namespace safemath { |
| 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 = checked_cast<int32_t>(x); |
| int32_t y_i32 = checked_cast<int32_t>(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 = checked_cast<int32_t>(x); |
| int32_t y_i32 = checked_cast<int32_t>(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 safemath |
| |
| #endif // SAFEMATH_SAFE_MATH_ARM_IMPL_H_ |