Mirror of :pserver:cvs@cvs.fefe.de:/cvs libowfat https://www.fefe.de/libowfat/
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.

#### 87 lines 2.0 KiB Raw Permalink Blame History

 ``````#include "fmt.h" size_t fmt_double(char *dest, double d,int maxlen,int prec) { union { double d; unsigned long long x; } __u = { .d=d, }; /* step 1: extract sign, mantissa and exponent */ signed int s=__u.x>>63; signed long e=((__u.x>>52)&((1<<11)-1))-1023; /* unsigned long long m=*x & ((1ull<<52)-1); */ /* step 2: exponent is base 2, compute exponent for base 10 */ signed long e10=1+(long)(e*0.30102999566398119802); /* log10(2) */ /* step 3: calculate 10^e10 */ int i; double tmp=10.0; char *oldbuf=dest; int initial=1; int writeok=(dest!=0); if (s) { d=-d; if (writeok) *dest='-'; --maxlen; dest++; } if (d==0.0) { if (writeok) *dest='0'; --maxlen; dest++; return dest-oldbuf; } if ((i=e10)>=0) { while (i>10) { tmp=tmp*1e10; i-=10; } while (i>1) { tmp=tmp*10; --i; } } else { i=(e10=-e10); while (i>10) { tmp=tmp*1e-10; i-=10; } while (i>1) { tmp=tmp/10; --i; } } while (d/tmp<1) { --e10; tmp/=10.0; } /* step 4: see if precision is sufficient to display all digits */ if (e10>prec) { /* use scientific notation */ int len=fmt_double(writeok?dest:0,d/tmp,maxlen,prec); if (len==0) return 0; maxlen-=len; dest+=len; if (--maxlen>=0) { if (writeok) *dest='e'; ++dest; } for (len=1000; len>0; len/=10) { if (e10>=len || !initial) { if (--maxlen>=0) { if (writeok) *dest=(e10/len)+'0'; ++dest; } initial=0; e10=e10%len; } } if (maxlen>=0) return dest-oldbuf; return 0; } /* step 5: loop through the digits, inserting the decimal point when * appropriate */ for (; prec>0; ) { double tmp2=d/tmp; char c; d-=((int)tmp2*tmp); c=((int)tmp2); if ((!initial)||c) { if (--maxlen>=0) { initial=0; if (writeok) *dest=c+'0'; ++dest; } else return 0; --prec; } if (tmp>0.5 && tmp<1.5) { tmp=1e-1; initial=0; if (--maxlen>=0) { if (writeok) *dest='.'; ++dest; } else return 0; } else tmp/=10.0; } return dest-oldbuf; }``````