3.74 Find Range II

★★

Write a function in assembly code that matches the behavior of the function find_range in Figure 3.51. Your code should contain only one floating-point comparison instruction, and then it should use conditional moves to generate the correct result. You might want to make use of instruction cmovp (move if even parity). Test your code on all 2^32 possible argument values.

Code:

#include <stdio.h>
#include <assert.h>

typedef enum {NEG, ZERO, POS, OTHER} range_t;

range_t find_range(float x) {
  __asm__(
      "vxorps %xmm1, %xmm1, %xmm1\n\t"
      "movq $1, %rax\n\t"
      "movq $2, %r8\n\t"
      "movq $0, %r9\n\t"
      "movq $3, %r10\n\t"
      "vucomiss %xmm1, %xmm0\n\t"
      "cmovaq %r8, %rax\n\t"
      "cmovbq %r9, %rax\n\t"
      "cmovpq %r10, %rax\n\t"
      );
}

int main(int argc, char* argv[]) {
    range_t n = NEG, z = ZERO, p = POS, o = OTHER;
    assert(o == find_range(0.0/0.0));
    assert(n == find_range(-2.3));
    assert(z == find_range(0.0));
    assert(p == find_range(3.33));
    return 0;
}