2.90

/*
 * fpwr2.c
 */
#include <stdio.h>
#include <assert.h>
#include <math.h>

float u2f(unsigned x) {
  return *(float*) &x;
}

/* 2^x */
float fpwr2(int x) {
  /* Result exponent and fraction */
  unsigned exp, frac;
  unsigned u;

  if (x < 2-pow(2,7)-23) {
    /* too small. return 0.0 */
    exp = 0;
    frac = 0;
  } else if (x < 2-pow(2,7)) {
    /* Denormalized result */
    exp = 0;
    frac = 1 << (unsigned)(x - (2-pow(2,7)-23));
  } else if (x < pow(2,7)-1+1) {
    /* Normalized result */
    exp = pow(2,7)-1+x;
    frac = 0;
  } else {
    /* Too big, return +oo */
    exp = 0xFF;
    frac = 0;
  }

  /* pack exp and frac into 32 bits */
  u = exp << 23 | frac;
  /* Result as float */
  return u2f(u);
}

int main(int argc, char* argv[]) {
  assert(fpwr2(0) == powf(2,0));
  assert(fpwr2(100) == powf(2,100));
  assert(fpwr2(-100) == powf(2,-100));
  assert(fpwr2(10000) == powf(2,10000));
  assert(fpwr2(-10000) == powf(2,-10000));
  return 0;
}