softfloat/s_estimateSqrt32.c

   1
   2 #include <stdint.h>
   3 #include "platform.h"
   4 #include "primitives.h"
   5
   6 uint32_t softfloat_estimateSqrt32( unsigned int expA, uint32_t a )
   7 {
   8     static const uint16_t sqrtOddAdjustments[] = {
   9         0x0004, 0x0022, 0x005D, 0x00B1, 0x011D, 0x019F, 0x0236, 0x02E0,
  10         0x039C, 0x0468, 0x0545, 0x0631, 0x072B, 0x0832, 0x0946, 0x0A67
  11     };
  12     static const uint16_t sqrtEvenAdjustments[] = {
  13         0x0A2D, 0x08AF, 0x075A, 0x0629, 0x051A, 0x0429, 0x0356, 0x029E,
  14         0x0200, 0x0179, 0x0109, 0x00AF, 0x0068, 0x0034, 0x0012, 0x0002
  15     };
  16     int index;
  17     uint32_t z;
  18     union { uint32_t ui; int32_t i; } u32;
  19
  20     index = ( a>>27 ) & 15;
  21     if ( expA & 1 ) {
  22         z = 0x4000 + ( a>>17 ) - sqrtOddAdjustments[ index ];
  23         z = ( ( a / z )<<14 ) + ( z<<15 );
  24         a >>= 1;
  25     } else {
  26         z = 0x8000 + ( a>>17 ) - sqrtEvenAdjustments[ index ];
  27         z = a / z + z;
  28         z = ( 0x20000 <= z ) ? 0xFFFF8000 : z<<15;
  29         if ( z <= a ) {
  30             u32.ui = a;
  31             return u32.i>>1;
  32         }
  33     }
  34     return (uint32_t) ( ( (uint64_t) a<<31 ) / z ) + ( z>>1 );
  35
  36 }
  37