/**
 * ieee.c
 *   A library of functions for exploring IEEE floating point numbers.
 */

// +---------+--------------------------------------------------------
// | Headers |
// +---------+

#include <stdio.h>
#include <math.h>       // For pow

#include "ieee.h"       
#include "bit-utils.h"	


// +---------+--------------------------------------------------------
// | Helpers |
// +---------+

/**
 * Get the bits for the significand.
 */
int
ieee32_significand_bits (float f)
{
  return f2i (f) & 0x7FFFFF;	// That's 0000000 01111111 11111111 11111111
} // ieee32_significand_bits


// +--------------------+---------------------------------------------
// | Exported Functions |
// +--------------------+

int
ieee32_sign (float f)
{
  return ith_bit (f2i (f), 31);
} // ieee32_sign

int
ieee32_exponent (float f)
{
  int exponent;
  exponent = f2i (f);
  // Drop the left bit
  exponent = zero_bit (exponent, 31);
  // Shift bits over so that they're in the convenient place
  exponent = exponent >> 23;
  // Subtract the bias
  exponent = exponent - 127;
  // And we're done
  return exponent;
} // ieee32_exponent

float
ieee32_significand (float f, int hidden)
{
  int bits = ieee32_significand_bits (f); // Bits of significand
  float result = (float) hidden;        // Result we're computing
  int i;                                // The bit we're looking at
  float value = 0.5;                    // The value of that bit.

  for (i = 22; i >= 0; i--)
    {
      // If the bit is set, add its value
      if (ith_bit (bits, i))
        result += value;
      // Move to the next value
      value /= 2.0;
    } // for

  // And we're done
  return result;
} // ieee32_significand

float
ieee32_significand_hack (float f, int hidden)
{
  int bits = ieee32_significand_bits (f);
  if (hidden) 
    bits = bits | 1 << 23;
  return bits / pow (2, 23);
} // ieee32_significand_hack

void
describe_float (float f)
{
  int sign;             // The sign of the number
  int exponent;         // The exponent of the number
  float significand;    // The significand
  int small;            // Special case: Really small numbers

  // Print it
  printf ("Exploring floating point number %f:\n", f);

  // Get the sign
  sign = ieee32_sign (f);

  // Get the exponent
  exponent = ieee32_exponent (f);

  // Handle special values
  if (exponent == 128)
    {
      // Infinities
      if (ieee32_significand_bits (f) == 0)
        {
          if (sign)
            printf ("  Negative infinity\n");
          else
            printf ("  Positive infinity\n");
        } // infinite
      else
        printf ("Not a number\n");
      return;
    } // special values

  // Determine if it's small
  small = exponent == -127;

  // Get the significand
  significand = ieee32_significand (f, !small);

  // Special case: Small numbers
  if (exponent == -127)
    exponent = -126;

  printf ("  Sign: %s\n", sign ? "-" : "+");
  printf ("  Exponent: %d\n", exponent);
  printf ("  Significand: %f\n", significand);
  printf ("  Significand2: %f\n", ieee32_significand_hack (f, !small));
} // describe_float