ref: 4d919ab612f61c1ef1b21d41513f264d57c010d4
dir: /sys/src/ape/lib/ap/stdio/ftoa.c/
#include <math.h> #include <stdlib.h> double pow10(int); #define NDIG 18 #define NFTOA (NDIG+4) /* * convert floating to ascii. ftoa returns an integer e such that * f=g*10**e, with .1<=|g|<1 (e=0 when g==0) and puts an ascii * representation of g in the buffer pointed to by bp. bp[0] will * be '+' or '-', and bp[1] to bp[NFTOA-2] * will be appropriate digits of g. bp[NFTOA-1] will be '\0' */ int ftoa(double f, char *bp){ int e, e1, e2, i; double digit, g, p; if(f>=0) *bp++='+'; else{ f=-f; *bp++='-'; } /* find e such that f==0 or 1<=f*pow10(e)<10, and set f=f*pow10(e) */ if(f==0.) e=1; else{ frexp(f, &e); e=-e*30103/100000; /* split in 2 pieces to guard against overflow in extreme cases */ e1=e/2; e2=e-e1; p=f*pow10(e2); while((g=p*pow10(e1))<1.) e1++; while((g=p*pow10(e1))>=10.) --e1; e=e1+e2; f=g; } for(i=0;i!=NDIG;i++){ f=modf(f, &digit)*10.; *bp++=digit+'0'; } *bp='\0'; return 1-e; }