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-rw-r--r-- | security/sandbox/chromium/base/numerics/safe_math_arm_impl.h | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/numerics/safe_math_arm_impl.h b/security/sandbox/chromium/base/numerics/safe_math_arm_impl.h new file mode 100644 index 0000000000..ff86bd0b73 --- /dev/null +++ b/security/sandbox/chromium/base/numerics/safe_math_arm_impl.h @@ -0,0 +1,122 @@ +// 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 = 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 base + +#endif // BASE_NUMERICS_SAFE_MATH_ARM_IMPL_H_ |