e5c844eff2
- Smaller C: fix a bug in __func__ introduced with
float-related changes
- make *printf() print floats greater than 1e25
- make *printf() print the plus sign when the format
includes "+", e.g. printf("%+f\n", 1.0);
- clean up and complete prototypes in <math.h>
- remove non-standard HUGE and LOGHUGE from <math.h>
- add HUGE_VAL to <math.h>
- express some hard-coded limits in terms of constants
from <float.h>
- uncomment prototypes of several floating point
conversion functions in <stdlib.h> for Smaller C
104 lines
1.7 KiB
C
104 lines
1.7 KiB
C
/*
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* floating point Bessel's function of
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* the first and second kinds and of integer order.
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*
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* int n;
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* double x;
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* jn(n,x);
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*
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* returns the value of Jn(x) for all
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* integer values of n and all real values of x.
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*
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* There are no error returns.
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* Calls j0, j1.
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*
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* For n=0, j0(x) is called,
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* for n=1, j1(x) is called,
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* for n<x, forward recursion us used starting
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* from values of j0(x) and j1(x).
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* for n>x, a continued fraction approximation to
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* j(n,x)/j(n-1,x) is evaluated and then backward
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* recursion is used starting from a supposed value
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* for j(n,x). The resulting value of j(0,x) is
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* compared with the actual value to correct the
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* supposed value of j(n,x).
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*
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* yn(n,x) is similar in all respects, except
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* that forward recursion is used for all values of n>1.
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*/
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#include <math.h>
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#include <errno.h>
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int errno;
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double
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jn(n,x) int n; double x;{
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int i;
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double a, b, temp;
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double xsq, t;
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double j0(), j1();
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if(n<0){
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n = -n;
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x = -x;
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}
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if(n==0) return(j0(x));
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if(n==1) return(j1(x));
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if(x == 0.) return(0.);
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if(n>x) goto recurs;
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a = j0(x);
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b = j1(x);
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for(i=1;i<n;i++){
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temp = b;
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b = (2.*i/x)*b - a;
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a = temp;
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}
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return(b);
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recurs:
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xsq = x*x;
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for(t=0,i=n+16;i>n;i--){
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t = xsq/(2.*i - t);
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}
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t = x/(2.*n-t);
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a = t;
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b = 1;
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for(i=n-1;i>0;i--){
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temp = b;
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b = (2.*i/x)*b - a;
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a = temp;
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}
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return(t*j0(x)/b);
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}
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double
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yn(n,x) int n; double x;{
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int i;
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int sign;
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double a, b, temp;
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double y0(), y1();
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if (x <= 0) {
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errno = EDOM;
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return(-HUGE_VAL);
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}
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sign = 1;
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if(n<0){
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n = -n;
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if(n%2 == 1) sign = -1;
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}
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if(n==0) return(y0(x));
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if(n==1) return(sign*y1(x));
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a = y0(x);
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b = y1(x);
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for(i=1;i<n;i++){
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temp = b;
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b = (2.*i/x)*b - a;
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a = temp;
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}
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return(sign*b);
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}
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