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  1. #include <stdio.h>
  2.  
  3. unsigned int2hfloat(int x)
  4. {
  5.   unsigned sign = x < 0;
  6.   unsigned absx = ((unsigned)x ^ -sign) + sign; // safe abs(x)
  7.   unsigned tmp = absx, manbits = 0;
  8.   int exp = 0, truncated = 0;
  9.  
  10.   // calculate the number of bits needed for the mantissa
  11.   while (tmp)
  12.   {
  13.     tmp >>= 1;
  14.     manbits++;
  15.   }
  16.  
  17.   // half-precision floats have 11 bits in the mantissa.
  18.   // truncate the excess or insert the lacking 0s until there are 11.
  19.   if (manbits)
  20.   {
  21.     exp = 10; // exp bias because 1.0 is at bit position 10
  22.     while (manbits > 11)
  23.     {
  24.       truncated |= absx & 1;
  25.       absx >>= 1;
  26.       manbits--;
  27.       exp++;
  28.     }
  29.     while (manbits < 11)
  30.     {
  31.       absx <<= 1;
  32.       manbits++;
  33.       exp--;
  34.     }
  35.   }
  36.  
  37.   if (exp + truncated > 15)
  38.   {
  39.     // absx was too big, force it to +/- infinity
  40.     exp = 31; // special infinity value
  41.     absx = 0;
  42.   }
  43.   else if (manbits)
  44.   {
  45.     // normal case, absx > 0
  46.     exp += 15; // bias the exponent
  47.   }
  48.  
  49.   return (sign << 15) | ((unsigned)exp << 10) | (absx & ((1u<<10)-1));
  50. }
  51.  
  52. int main(void)
  53. {
  54.   printf(" 0: 0x%04X\n", int2hfloat(0));
  55.   printf("-1: 0x%04X\n", int2hfloat(-1));
  56.   printf("+1: 0x%04X\n", int2hfloat(+1));
  57.   printf("-2: 0x%04X\n", int2hfloat(-2));
  58.   printf("+2: 0x%04X\n", int2hfloat(+2));
  59.   printf("-3: 0x%04X\n", int2hfloat(-3));
  60.   printf("+3: 0x%04X\n", int2hfloat(+3));
  61.   printf("-2047: 0x%04X\n", int2hfloat(-2047));
  62.   printf("+2047: 0x%04X\n", int2hfloat(+2047));
  63.   printf("-2048: 0x%04X\n", int2hfloat(-2048));
  64.   printf("+2048: 0x%04X\n", int2hfloat(+2048));
  65.   printf("-2049: 0x%04X\n", int2hfloat(-2049)); // first inexact integer
  66.   printf("+2049: 0x%04X\n", int2hfloat(+2049));
  67.   printf("-2050: 0x%04X\n", int2hfloat(-2050));
  68.   printf("+2050: 0x%04X\n", int2hfloat(+2050));
  69.   printf("-32752: 0x%04X\n", int2hfloat(-32752));
  70.   printf("+32752: 0x%04X\n", int2hfloat(+32752));
  71.   printf("-32768: 0x%04X\n", int2hfloat(-32768));
  72.   printf("+32768: 0x%04X\n", int2hfloat(+32768));
  73.   printf("-65504: 0x%04X\n", int2hfloat(-65504)); // legal maximum
  74.   printf("+65504: 0x%04X\n", int2hfloat(+65504));
  75.   printf("-65505: 0x%04X\n", int2hfloat(-65505)); // infinity from here on
  76.   printf("+65505: 0x%04X\n", int2hfloat(+65505));
  77.   printf("-65535: 0x%04X\n", int2hfloat(-65535));
  78.   printf("+65535: 0x%04X\n", int2hfloat(+65535));
  79.   return 0;
  80. }
  81.  
Success #stdin #stdout 0.02s 1676KB
comments (?)
stdin 
Standard input is empty
stdout 
 0: 0x0000
-1: 0xBC00
+1: 0x3C00
-2: 0xC000
+2: 0x4000
-3: 0xC200
+3: 0x4200
-2047: 0xE7FF
+2047: 0x67FF
-2048: 0xE800
+2048: 0x6800
-2049: 0xE800
+2049: 0x6800
-2050: 0xE801
+2050: 0x6801
-32752: 0xF7FF
+32752: 0x77FF
-32768: 0xF800
+32768: 0x7800
-65504: 0xFBFF
+65504: 0x7BFF
-65505: 0xFC00
+65505: 0x7C00
-65535: 0xFC00
+65535: 0x7C00
https://ideone.com/2LXt8
language:
C99 (gcc 8.3)
created:
11 years ago
visibility:
public

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