overflow.h

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#pragma once
 
#include <assert.h>
#include <limits.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
 
static inline bool sadd_overflow(int a, int b, int *res) {
  assert(res != NULL);
 
  // delegate to hardware optimized implementations where possible
#if defined(__clang__) &&                                                      \
    (__clang_major__ > 3 ||                                                    \
     (__clang_major__ == 3 && __clang_minor__ > 7)) // Clang ≥ 3.8
  return __builtin_sadd_overflow(a, b, res);
#elif defined(__GNUC__) && __GNUC__ > 4 // GCC ≥ 5
  return __builtin_sadd_overflow(a, b, res);
#endif
 
  if (a > 0 && INT_MAX - a < b) {
    return true;
  }
  if (a < 0 && INT_MIN - a > b) {
    return true;
  }
 
  *res = a + b;
  return false;
}
 
static inline bool u64add_overflow(uint64_t a, uint64_t b, uint64_t *res) {
  assert(res != NULL);
 
  // delegate to hardware optimized implementations where possible
#if defined(__clang__) &&                                                      \
    (__clang_major__ > 3 ||                                                    \
     (__clang_major__ == 3 && __clang_minor__ > 7)) // Clang ≥ 3.8
  return __builtin_add_overflow(a, b, res);
#elif defined(__GNUC__) && __GNUC__ > 4 // GCC ≥ 5
  return __builtin_add_overflow(a, b, res);
#endif
 
  if (UINT64_MAX - a < b) {
    return true;
  }
 
  *res = a + b;
  return false;
}
 
static inline bool u64mul_overflow(uint64_t a, uint64_t b, uint64_t *res) {
  assert(res != NULL);
 
  // delegate to hardware optimized implementations where possible
#if defined(__clang__) &&                                                      \
    (__clang_major__ > 3 ||                                                    \
     (__clang_major__ == 3 && __clang_minor__ > 7)) // Clang ≥ 3.8
  return __builtin_mul_overflow(a, b, res);
#elif defined(__GNUC__) && __GNUC__ > 4 // GCC ≥ 5
  return __builtin_mul_overflow(a, b, res);
#endif
 
  if (a > 0 && UINT64_MAX / a < b) {
    return true;
  }
 
  *res = a * b;
  return false;
}