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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.   // round the number if necessary before we do the conversion
  18.   if (manbits > 13)
  19.     absx += (2<<(manbits-13));
  20.  
  21.   manbits = 0;
  22.   tmp = absx;
  23.   while (tmp)
  24.   {
  25.     tmp >>= 1;
  26.     manbits++;
  27.   }
  28.  
  29.   // half-precision floats have 11 bits in the mantissa.
  30.   // truncate the excess or insert the lacking 0s until there are 11.
  31.   if (manbits)
  32.   {
  33.     exp = 10; // exp bias because 1.0 is at bit position 10
  34.     while (manbits > 11)
  35.     {
  36.       truncated |= absx & 1;
  37.       absx >>= 1;
  38.       manbits--;
  39.       exp++;
  40.     }
  41.     while (manbits < 11)
  42.     {
  43.       absx <<= 1;
  44.       manbits++;
  45.       exp--;
  46.     }
  47.   }
  48.   if (exp + truncated > 16)
  49.   {
  50.     // absx was too big, force it to +/- infinity
  51.     exp = 31; // special infinity value
  52.     absx = 0;
  53.   }
  54.   else if (manbits)
  55.   {
  56.     // normal case, absx > 0
  57.     exp += 15; // bias the exponent
  58.   }
  59.  
  60.   return (sign << 15) | ((unsigned)exp << 10) | (absx & ((1u<<10)-1));
  61. }
  62.  
  63. int main(void)
  64. {
  65.   printf("+4095: 0x%04X\n", int2hfloat(+4095));
  66.   printf("+4096: 0x%04X\n", int2hfloat(+4096));
  67.   printf("+4097: 0x%04X\n", int2hfloat(+4097));
  68.   printf("+4098: 0x%04X\n", int2hfloat(+4098));
  69.   printf("+4099: 0x%04X\n", int2hfloat(+4099));
  70.   printf("+2052: 0x%04X\n", int2hfloat(+2052));
  71.   printf("+8190: 0x%04X\n", int2hfloat(+8190));
  72.   printf("+8191: 0x%04X\n", int2hfloat(+8191));
  73.   printf("+8192: 0x%04X\n", int2hfloat(+8192));
  74.   printf("+8193: 0x%04X\n", int2hfloat(+8193));
  75.   printf("+8194: 0x%04X\n", int2hfloat(+8194));
  76.   printf("+8195: 0x%04X\n", int2hfloat(+8195));
  77.   printf("+8196: 0x%04X\n", int2hfloat(+8196));
  78.   printf("+8197: 0x%04X\n", int2hfloat(+8197));
  79.   printf("+8198: 0x%04X\n", int2hfloat(+8198));
  80.   printf("+8199: 0x%04X\n", int2hfloat(+8199));
  81.   printf("+8200: 0x%04X\n", int2hfloat(+8200));
  82.   printf("+16398: 0x%04X\n", int2hfloat(+16398));
  83.   printf("+16400: 0x%04X\n", int2hfloat(+16400));
  84.   printf("+32768: 0x%04X\n", int2hfloat(+32768));
  85.   printf("+65504: 0x%04X\n", int2hfloat(+65504));
  86.   printf("+65505: 0x%04X\n", int2hfloat(+65505));
  87.   printf("+65519: 0x%04X\n", int2hfloat(+65519));
  88.   printf("+65534: 0x%04X\n", int2hfloat(+65534));
  89.   printf("+65535: 0x%04X\n", int2hfloat(+65535));
  90.   printf("+65535: 0x%04X\n", int2hfloat(+65536));
  91.   return 0;
  92. }
  93.  
Success #stdin #stdout 0s 4504KB
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stdin
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Standard input is empty
stdout
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+4095: 0x6BFF
+4096: 0x6C00
+4097: 0x6C00
+4098: 0x6C00
+4099: 0x6C00
+2052: 0x6802
+8190: 0x6FFF
+8191: 0x6FFF
+8192: 0x7000
+8193: 0x7000
+8194: 0x7000
+8195: 0x7000
+8196: 0x7001
+8197: 0x7001
+8198: 0x7001
+8199: 0x7001
+8200: 0x7001
+16398: 0x7401
+16400: 0x7401
+32768: 0x7800
+65504: 0x7BFF
+65505: 0x7BFF
+65519: 0x7BFF
+65534: 0x7C00
+65535: 0x7C00
+65535: 0x7C00
https://ideone.com/mWqgSP
language:
C99 (gcc 8.3)
created:
5 years ago
visibility:
public

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