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#include "test.h"
#include <stdint.h>
#include <stdbool.h>
bool multiply_with_overflow(uint32_t a, uint32_t b, uint32_t *result) {
uint32_t res, m_overflow;
// Use GCC inline assembly to do: res = a * b, with overflow in m_overflow
asm volatile (
"mull %3" // Multiply EAX by operand %3 → result in EDX:EAX
: "=&a"(res), "=&d"(m_overflow) // outputs: EAX → res, EDX → m_overflow
: "a"(a), "rm"(b) // inputs: a in EAX, b in reg/mem
);
*result = res;
return m_overflow != 0;
}
int main(void) {
uint32_t a = 0xFFFFFFFF;
uint32_t b = 2;
uint32_t res;
bool overflow = multiply_with_overflow(a, b, &res);
printf("Result: %u (0x%08x)\n", res, res);
printf("Overflow: %s\n", overflow ? "Yes" : "No");
ASSERT(1, overflow);
ASSERT(0xfffffffe, res);
uint32_t nmemb = 0xFFFFFFFE;
uint32_t size = 2;
uint32_t offset = 1;
uint32_t resm = nmemb;
uint32_t m_overflow;
__asm__ volatile (
"mull %3\n\t"
"add %4, %0\n\t"
"adc $0, %1"
: "=&a"(resm), "=&d"(m_overflow)
: "%0"(resm), "rm"(size), "rm"(offset)
: "cc"
);
printf("Result: %u (0x%08x)\n", resm, resm);
printf("Overflow: %u\n", m_overflow);
ASSERT(1, m_overflow);
ASSERT(0xfffffffd, resm);
return 0;
}
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