thodg/libgit2/src/integer.h

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• Hash : e99e833f
  Author :
  Date : 2020-12-12T16:51:15
  

  Make git__strntol64() ~70%* faster This change uses compiler intrinsics to detect overflows instead of using divisions to detect potential overflow. This makes the code faster and makes it easier to read as a bonus side-effect! Some of the things this quickens: * Config parsing. * Tree parsing. * Smart protocol negotiation. \* Measured by running `libgit2_clar` with `-fno-optimize-sibling-calls -fno-omit-frame-pointer` under `perf(1)`: ```shell $ perf diff --symbols=git__strntol64 --compute=ratio \ --percentage=absolute baseline.data perf.data \# Event 'cycles' \# \# Baseline Ratio Shared Object \# ........ .............. ............. \# 0.25% 0.321836 libgit2_clar ```

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• src/integer.h

• /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   */
  #ifndef INCLUDE_integer_h__
  #define INCLUDE_integer_h__
  
  /** @return true if p fits into the range of a size_t */
  GIT_INLINE(int) git__is_sizet(int64_t p)
  {
  	size_t r = (size_t)p;
  	return p == (int64_t)r;
  }
  
  /** @return true if p fits into the range of an ssize_t */
  GIT_INLINE(int) git__is_ssizet(size_t p)
  {
  	ssize_t r = (ssize_t)p;
  	return p == (size_t)r;
  }
  
  /** @return true if p fits into the range of a uint16_t */
  GIT_INLINE(int) git__is_uint16(size_t p)
  {
  	uint16_t r = (uint16_t)p;
  	return p == (size_t)r;
  }
  
  /** @return true if p fits into the range of a uint32_t */
  GIT_INLINE(int) git__is_uint32(size_t p)
  {
  	uint32_t r = (uint32_t)p;
  	return p == (size_t)r;
  }
  
  /** @return true if p fits into the range of an unsigned long */
  GIT_INLINE(int) git__is_ulong(int64_t p)
  {
  	unsigned long r = (unsigned long)p;
  	return p == (int64_t)r;
  }
  
  /** @return true if p fits into the range of an int */
  GIT_INLINE(int) git__is_int(long long p)
  {
  	int r = (int)p;
  	return p == (long long)r;
  }
  
  /* Use clang/gcc compiler intrinsics whenever possible */
  #if (__has_builtin(__builtin_add_overflow) || \
       (defined(__GNUC__) && (__GNUC__ >= 5)))
  
  # if (SIZE_MAX == UINT_MAX)
  #  define git__add_sizet_overflow(out, one, two) \
       __builtin_uadd_overflow(one, two, out)
  #  define git__multiply_sizet_overflow(out, one, two) \
       __builtin_umul_overflow(one, two, out)
  # elif (SIZE_MAX == ULONG_MAX)
  #  define git__add_sizet_overflow(out, one, two) \
       __builtin_uaddl_overflow(one, two, out)
  #  define git__multiply_sizet_overflow(out, one, two) \
       __builtin_umull_overflow(one, two, out)
  # elif (SIZE_MAX == ULLONG_MAX)
  #  define git__add_sizet_overflow(out, one, two) \
       __builtin_uaddll_overflow(one, two, out)
  #  define git__multiply_sizet_overflow(out, one, two) \
       __builtin_umulll_overflow(one, two, out)
  # else
  #  error compiler has add with overflow intrinsics but SIZE_MAX is unknown
  # endif
  
  # define git__add_int_overflow(out, one, two) \
      __builtin_sadd_overflow(one, two, out)
  # define git__sub_int_overflow(out, one, two) \
      __builtin_ssub_overflow(one, two, out)
  
  # define git__add_int64_overflow(out, one, two) \
      __builtin_add_overflow(one, two, out)
  # define git__multiply_int64_overflow(out, one, two) \
      __builtin_mul_overflow(one, two, out)
  
  /* Use Microsoft's safe integer handling functions where available */
  #elif defined(_MSC_VER)
  
  # define ENABLE_INTSAFE_SIGNED_FUNCTIONS
  # include <intsafe.h>
  
  # define git__add_sizet_overflow(out, one, two) \
      (SizeTAdd(one, two, out) != S_OK)
  # define git__multiply_sizet_overflow(out, one, two) \
      (SizeTMult(one, two, out) != S_OK)
  
  #define git__add_int_overflow(out, one, two) \
      (IntAdd(one, two, out) != S_OK)
  #define git__sub_int_overflow(out, one, two) \
      (IntSub(one, two, out) != S_OK)
  
  #define git__add_int64_overflow(out, one, two) \
      (LongLongAdd(one, two, out) != S_OK)
  #define git__multiply_int64_overflow(out, one, two) \
      (LongLongMult(one, two, out) != S_OK)
  
  #else
  
  /**
   * Sets `one + two` into `out`, unless the arithmetic would overflow.
   * @return false if the result fits in a `size_t`, true on overflow.
   */
  GIT_INLINE(bool) git__add_sizet_overflow(size_t *out, size_t one, size_t two)
  {
  	if (SIZE_MAX - one < two)
  		return true;
  	*out = one + two;
  	return false;
  }
  
  /**
   * Sets `one * two` into `out`, unless the arithmetic would overflow.
   * @return false if the result fits in a `size_t`, true on overflow.
   */
  GIT_INLINE(bool) git__multiply_sizet_overflow(size_t *out, size_t one, size_t two)
  {
  	if (one && SIZE_MAX / one < two)
  		return true;
  	*out = one * two;
  	return false;
  }
  
  GIT_INLINE(bool) git__add_int_overflow(int *out, int one, int two)
  {
  	if ((two > 0 && one > (INT_MAX - two)) ||
  	    (two < 0 && one < (INT_MIN - two)))
  		return true;
  	*out = one + two;
  	return false;
  }
  
  GIT_INLINE(bool) git__sub_int_overflow(int *out, int one, int two)
  {
  	if ((two > 0 && one < (INT_MIN + two)) ||
  	    (two < 0 && one > (INT_MAX + two)))
  		return true;
  	*out = one - two;
  	return false;
  }
  
  GIT_INLINE(bool) git__add_int64_overflow(int64_t *out, int64_t one, int64_t two)
  {
  	if ((two > 0 && one > (INT64_MAX - two)) ||
  	    (two < 0 && one < (INT64_MIN - two)))
  		return true;
  	*out = one + two;
  	return false;
  }
  
  GIT_INLINE(bool) git__multiply_int64_overflow(int64_t *out, int64_t one, int64_t two)
  {
  	if ((one == -1 && two == INT_MIN) ||
  	    (two == -1 && one == INT_MIN) ||
  	    (one && INT64_MAX / one < two) ||
  	    (one && INT64_MIN / one > two))
  		return true;
  	*out = one * two;
  	return false;
  }
  
  #endif
  
  #endif
  

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