Compiler Explorer

Source code

#include <stdint.h>
#include <assert.h>
typedef unsigned __int128 uint128_t;

#define muladd_fast_new(a,b) { \
    uint128_t t = (uint128_t)a * b + c0; \
    c0 = (uint64_t)t; \
    c1 += (uint64_t)(t >> 64);  /* never overflows by contract (verified in the next line) */ \
    assert(c1 >= t >> 64); \
}

#define muladd_fast(a,b) { \
    uint64_t tl, th; \
    { \
        uint128_t t = (uint128_t)a * b; \
        th = t >> 64;         /* at most 0xFFFFFFFFFFFFFFFE */ \
        tl = t; \
    } \
    c0 += tl;                 /* overflow is handled on the next line */ \
    th += (c0 < tl) ? 1 : 0;  /* at most 0xFFFFFFFFFFFFFFFF */ \
    c1 += th;                 /* never overflows by contract (verified in the next line) */ \
    assert(c1 >= th); \
}

// Type your code here, or load an example.
int old(uint64_t a, uint64_t b,uint64_t c, uint64_t d,uint64_t c0, uint64_t c1 ) {
    muladd_fast(a,b);
    muladd_fast(c,d);

return c0+c1*3454546;
}

int new(uint64_t a, uint64_t b, uint64_t c, uint64_t d, uint64_t c0, uint64_t c1) {
    muladd_fast_new(a,b);
    muladd_fast_new(c,d);
    
    return c0+c1*3454546;
}