Mirror of :pserver:cvs@cvs.fefe.de:/cvs libowfat https://www.fefe.de/libowfat/
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#include "fmt.h"
unsigned int fmt_double(char *dest, double d,int maxlen,int prec) {
unsigned long long *x=(unsigned long long *)&d;
/* step 1: extract sign, mantissa and exponent */
signed int s=*x>>63;
signed long e=((*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 ((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;
}