kc3-lang/angle/src/common/base/anglebase/numerics/safe_math_arm_impl.h

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• Hash : c991eb22
  Author :
  Date : 2022-12-01T14:05:07
  

  Move the anglebase folder up a level
  
  This code originates from Chromium's base/ directory so it doesn't have
  to be under a third-party folder.
  
  Bug: b/260093525
  Change-Id: I0bf6950095c685f36c5c237093980a64cf6e74f0
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4068339
  Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
  Reviewed-by: Geoff Lang <geofflang@chromium.org>
  Reviewed-by: Jamie Madill <jmadill@chromium.org>
  Commit-Queue: Nicolas Capens <nicolascapens@google.com>
  

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• src/common/base/anglebase/numerics/safe_math_arm_impl.h

• // 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 <type_traits>
  
  #include "anglebase/numerics/safe_conversions.h"
  
  namespace angle
  {
  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);
          if (!IsValueInRangeForNumericType<V>(presult))
              return false;
          *result = static_cast<V>(presult);
          return true;
      }
  };
  
  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;
              return CheckedMulFastAsmOp<T, U>::Do(x, y, &result)
                         ? result
                         : 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
  }  // namespace angle
  
  #endif  // BASE_NUMERICS_SAFE_MATH_ARM_IMPL_H_
  

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