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#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
uint64_t mult(uint64_t x, uint64_t y, unsigned int bits) {
/* Check if they expect more than 64 bits. */
if( bits > 64 ) {
printf("Sorry we cant handle higher than 64 bits\n");
exit(1);
} else if(bits <= 1) {
return x && y;
}
unsigned int newBits = bits >> 1;
#if DO_PRINT == 1
printf("\n\n bits: %u, New bits: %u\n", bits, newBits);
#endif
/* Split up into to */
uint32_t halvMask = ((uint64_t)1 << newBits) - 1;
#if DO_PRINT == 1
printf("Using mask 0x%08X\n", halvMask);
#endif
uint32_t a = (x >> (newBits)) & halvMask;
uint32_t b = x & halvMask;
uint32_t c = (y >> (newBits)) & halvMask;
uint32_t d = y & halvMask;
#if DO_PRINT == 1
printf("A: 0x%08X, B: 0x%08X, C: 0x%08X, D: 0x%08X\n", a, b, c, d);
#endif
return (mult(a, c, newBits) << bits) + ((mult(a, d, newBits) + mult(b, c, newBits)) << newBits) + mult(b, d, newBits);
}
int main(void) {
uint32_t a = 0xFFFFFF;
uint8_t b = 55;
uint64_t res;
clock_t begin = clock();
res = mult(a, b, 64);
clock_t end = clock();
printf("Result: %lld\n", res);
clock_t diff = end - begin;
printf("Took %d which is %f s\n", diff, (double)diff/CLOCKS_PER_SEC);
return 0;
}
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