57 lines
759 B
C
57 lines
759 B
C
/*
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sqrt returns the square root of its floating
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point argument. Newton's method.
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calls frexp
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*/
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#include <math.h>
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#include <errno.h>
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#define _RESEARCH_SOURCE
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#include <float.h>
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double
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sqrt(double arg)
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{
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double x, temp;
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int exp, i;
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if(isInf(arg, 1))
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return arg;
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if(arg <= 0) {
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if(arg < 0)
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errno = EDOM;
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return 0;
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}
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x = frexp(arg, &exp);
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while(x < 0.5) {
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x *= 2;
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exp--;
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}
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/*
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* NOTE
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* this wont work on 1's comp
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*/
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if(exp & 1) {
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x *= 2;
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exp--;
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}
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temp = 0.5 * (1.0+x);
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while(exp > 60) {
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temp *= (1L<<30);
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exp -= 60;
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}
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while(exp < -60) {
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temp /= (1L<<30);
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exp += 60;
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}
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if(exp >= 0)
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temp *= 1L << (exp/2);
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else
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temp /= 1L << (-exp/2);
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for(i=0; i<=4; i++)
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temp = 0.5*(temp + arg/temp);
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return temp;
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}
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