Reciprocal estimate not accurate enough

[pmatos]

Currently on systems with rpres extension we generate frecpe for a pfrcp. The AMD manual mentions:

The maximum error is less than or equal to 1.5 * 2^–12 times the true reciprocal.

Unfortunately for, for example 1.0, the result of frecpe is 0.998047. The result should be within (1.00037 | 0.999634) to be within the required accuracy.

Should check other functions as well.

[pmatos]

Test:

#include <stdio.h>

int main(void) {
  float x = 1.0;

  float r;
  asm volatile("frecpe %s1, %s0" // 3DNow! reciprocal estimate
               : "=w"(r)         // Output: result (floating-point)
               : "w"(x)          // Input: x (floating-point)
  );
  printf("recip: %f\n", r);
  return 0;
}