glaux - Page 1

Orion_ a écrit :
les tutos et même Nehe, utilise Glaux !!! (glaux.lib, pas glaux.dll)

/******************************************************************************
*
* project name:  FAT-Engine
* file name:     fastsqrt.c
* initial date:  16/04/2002
* author:        thomas.nussbaumer@gmx.net
* description:   fast square root algorithm using a 256 bytes lookup table
*
* (algorithm posted at comp.graphics.algorithms)
*
* $Id: fastsqrt.c,v 1.1 2002/04/18 16:09:53 tnussb Exp $
*
******************************************************************************/

/*
// Integer Square Root function
// Contributors include Arne Steinarson for the basic approximation idea, Dann
// Corbit and Mathew Hendry for the first cut at the algorithm, Lawrence Kirby
// for the rearrangement, improvments and range optimization and Paul Hsieh
// for the round-then-adjust idea.
*/
unsigned long fastsqrt(unsigned long x) {
    static const unsigned char sqq_table[] = {
       0,  16,  22,  27,  32,  35,  39,  42,  45,  48,  50,  53,  55,  57,
      59,  61,  64,  65,  67,  69,  71,  73,  75,  76,  78,  80,  81,  83,
      84,  86,  87,  89,  90,  91,  93,  94,  96,  97,  98,  99, 101, 102,
     103, 104, 106, 107, 108, 109, 110, 112, 113, 114, 115, 116, 117, 118,
     119, 120, 121, 122, 123, 124, 125, 126, 128, 128, 129, 130, 131, 132,
     133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 144, 145,
     146, 147, 148, 149, 150, 150, 151, 152, 153, 154, 155, 155, 156, 157,
     158, 159, 160, 160, 161, 162, 163, 163, 164, 165, 166, 167, 167, 168,
     169, 170, 170, 171, 172, 173, 173, 174, 175, 176, 176, 177, 178, 178,
     179, 180, 181, 181, 182, 183, 183, 184, 185, 185, 186, 187, 187, 188,
     189, 189, 190, 191, 192, 192, 193, 193, 194, 195, 195, 196, 197, 197,
     198, 199, 199, 200, 201, 201, 202, 203, 203, 204, 204, 205, 206, 206,
     207, 208, 208, 209, 209, 210, 211, 211, 212, 212, 213, 214, 214, 215,
     215, 216, 217, 217, 218, 218, 219, 219, 220, 221, 221, 222, 222, 223,
     224, 224, 225, 225, 226, 226, 227, 227, 228, 229, 229, 230, 230, 231,
     231, 232, 232, 233, 234, 234, 235, 235, 236, 236, 237, 237, 238, 238,
     239, 240, 240, 241, 241, 242, 242, 243, 243, 244, 244, 245, 245, 246,
     246, 247, 247, 248, 248, 249, 249, 250, 250, 251, 251, 252, 252, 253,
     253, 254, 254, 255
    };

    unsigned long xn;

    if (x >= 0x10000) {
        if (x >= 0x1000000) {
            if (x >= 0x10000000) {
                if (x >= 0x40000000) {
                    if (x >= 65535UL*65535UL) return 65535;
                    xn = sqq_table[x>>24] << 8;
                }
                else {
                    xn = sqq_table[x>>22] << 7;
                }
            }
            else if (x >= 0x4000000) xn = sqq_table[x>>20] << 6;
            else                     xn = sqq_table[x>>18] << 5;
        }
        else {
            if (x >= 0x100000) {
                if (x >= 0x400000) xn = sqq_table[x>>16] << 4;
                else               xn = sqq_table[x>>14] << 3;
            }
            else {
                if (x >= 0x40000) xn = sqq_table[x>>12] << 2;
                else              xn = sqq_table[x>>10] << 1;
            }
            goto nr1;
        }
    }
    else if (x >= 0x100) {
        if (x >= 0x1000) {
            if (x >= 0x4000) xn = (sqq_table[x>>8] >> 0) + 1;
            else             xn = (sqq_table[x>>6] >> 1) + 1;
        }
        else if (x >= 0x400) xn = (sqq_table[x>>4] >> 2) + 1;
        else                 xn = (sqq_table[x>>2] >> 3) + 1;

        goto adj;
    }
    else {
        return sqq_table[x] >> 4;
    }

    xn = (xn + 1 + x / xn) >> 1;
nr1:
    xn = (xn + 1 + x / xn) >> 1;
adj:

    // we don't care about being one on the wrong side - therefore the
    // next line is commented out.

    // if (xn * xn > x) xn--;

    return xn;
}


//#############################################################################
// Revision History
//#############################################################################
//
// $Log: fastsqrt.c,v $
// Revision 1.1  2002/04/18 16:09:53  tnussb
// initial version
//
//