Category : C Source Code
Archive   : CEPHES22.ZIP
Filename : QSQRT.C

 
Output of file : QSQRT.C contained in archive : CEPHES22.ZIP
/* qsqrt.c */
/* square root check routine */
/* full precision for 9 word mantissa */
#include "qhead.h"
extern short qsqrt2[];

/* constants for first approximation polynomial */
static short qsq2[NQ] =
{-1,037776,0,0150517,0142057,0163633,0124000,0,0,0,0,0,};

static short qsq1[NQ] =
{0,040000,0,0161743,0141256,046024,063400,0,0,0,0,0,};

static short qsq0[NQ] =
{0,037777,0,0120213,0156175,0152777,0161400,0,0,0,0,0,};

int qsqrt( x, y )
short *x, *y;
{
short a[NQ], b[NQ];
int i, m;

if( x[0] < 0 )
{
qclear(y);
printf( "qsqrt domain error\n" );
return;
}
if( x[1] == 0 )
{
qclear(y);
return;
}

qmov( x, a );
m = a[1]; /* save the exponent */
a[1] = 040000; /* change range to 0.5, 1 */

/* b = ( a * qsq2 + qsq1) * a + qsq0 */
qmul( a, qsq2, b ); /* b = a * qsq2 */
qadd( qsq1, b, b ); /* b += qsq1 */
qmul( a, b, b ); /* b *= a; */
qadd( qsq0, b, b ); /* b += qsq0; */

/* divide exponent by 2 */
m -= 040000;
b[1] = (m / 2) + 040000;


/* multiply by sqrt(2) if exponent odd */
if( (m & 1) != 0 )
qmul( b, qsqrt2, b );


/* Newton iterations */

for( i=0; i<8; i++ )
{
qdiv( b, x, a );
qadd( a, b, b );
b[1] -= 1;
}

qmov( b, y );
}


  3 Responses to “Category : C Source Code
Archive   : CEPHES22.ZIP
Filename : QSQRT.C

  1. Very nice! Thank you for this wonderful archive. I wonder why I found it only now. Long live the BBS file archives!

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