cgm999/mul_a_weird.c

## mul_a_weird.c
#include <stdio.h>
#include <stdint.h>

uint16_t find_inv(uint16_t a) {
    uint16_t inv = 1;
    for (int i = 0; i < 16; i++) inv *= 2 - a * inv;
    return inv;
}

uint16_t mul_a,mul_a_inv;
uint16_t encode(uint16_t x) { return mul_a*x; }
uint16_t decode(uint16_t x) { return x * mul_a_inv; }

int main() {
   for(int i=65535;i;i--) {
      mul_a = i;
      mul_a_inv = find_inv(i);
      if(i&1) {
         printf("checking i=%d\n",i);
         for(int j=65535;j;j--) {
            uint16_t rev_j = decode(encode(j));
            if(j!=rev_j) printf("i=%d bad rev for j=%d\n",i,j);
         }
      }
   }
   return 0;
}
	#include <stdio.h>
	#include <stdint.h>

	uint16_t find_inv(uint16_t a) {
	uint16_t inv = 1;
	for (int i = 0; i < 16; i++) inv = 2 - a inv;
	return inv;
	}

	uint16_t mul_a,mul_a_inv;
	uint16_t encode(uint16_t x) { return mul_a*x; }
	uint16_t decode(uint16_t x) { return x * mul_a_inv; }

	int main() {
	for(int i=65535;i;i--) {
	mul_a = i;
	mul_a_inv = find_inv(i);
	if(i&1) {
	printf("checking i=%d\n",i);
	for(int j=65535;j;j--) {
	uint16_t rev_j = decode(encode(j));
	if(j!=rev_j) printf("i=%d bad rev for j=%d\n",i,j);
	}
	}
	}
	return 0;
	}
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