ref: 5d6ebf7a53a2992d56e7403afd5cfce59b15e879
dir: /libc/fltfmt.c/
#include <u.h>
#include <libc.h>
#include <ctype.h>
#include "fmtdef.h"
enum
{
FDIGIT = 30,
FDEFLT = 6,
NSIGNIF = 17,
};
static int
xadd(char *a, int n, int v)
{
char *b;
int c;
if(n < 0 || n >= NSIGNIF)
return 0;
for(b = a+n; b >= a; b--) {
c = *b + v;
if(c <= '9') {
*b = c;
return 0;
}
*b = '0';
v = 1;
}
*a = '1'; // overflow adding
return 1;
}
static int
xsub(char *a, int n, int v)
{
char *b;
int c;
for(b = a+n; b >= a; b--) {
c = *b - v;
if(c >= '0') {
*b = c;
return 0;
}
*b = '9';
v = 1;
}
*a = '9'; // underflow subtracting
return 1;
}
static void
xdtoa(Fmt *fmt, char *s2, double f)
{
char s1[NSIGNIF+10];
double g, h;
int e, d, i, n;
int c1, c2, c3, c4, ucase, sign, chr, prec;
prec = FDEFLT;
if(fmt->flags & FmtPrec)
prec = fmt->prec;
if(prec > FDIGIT)
prec = FDIGIT;
if(__isNaN(f)) {
strcpy(s2, "NaN");
return;
}
if(__isInf(f, 1)) {
strcpy(s2, "+Inf");
return;
}
if(__isInf(f, -1)) {
strcpy(s2, "-Inf");
return;
}
sign = 0;
if(f < 0) {
f = -f;
sign++;
}
ucase = 0;
chr = fmt->r;
if(isupper(chr)) {
ucase = 1;
chr = tolower(chr);
}
e = 0;
g = f;
if(g != 0) {
frexp(f, &e);
e = e * .301029995664;
if(e >= -150 && e <= +150) {
d = 0;
h = f;
} else {
d = e/2;
h = f * pow10(-d);
}
g = h * pow10(d-e);
while(g < 1) {
e--;
g = h * pow10(d-e);
}
while(g >= 10) {
e++;
g = h * pow10(d-e);
}
}
/*
* convert NSIGNIF digits and convert
* back to get accuracy.
*/
for(i=0; i<NSIGNIF; i++) {
d = g;
s1[i] = d + '0';
g = (g - d) * 10;
}
s1[i] = 0;
/*
* try decimal rounding to eliminate 9s
*/
c2 = prec + 1;
if(chr == 'f')
c2 += e;
if(c2 >= NSIGNIF-2) {
strcpy(s2, s1);
d = e;
s1[NSIGNIF-2] = '0';
s1[NSIGNIF-1] = '0';
sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
g = strtod(s1, nil);
if(g == f)
goto found;
if(xadd(s1, NSIGNIF-3, 1)) {
e++;
sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
}
g = strtod(s1, nil);
if(g == f)
goto found;
strcpy(s1, s2);
e = d;
}
/*
* convert back so s1 gets exact answer
*/
for(;;) {
sprint(s1+NSIGNIF, "e%d", e-NSIGNIF+1);
g = strtod(s1, nil);
if(f > g) {
if(xadd(s1, NSIGNIF-1, 1))
e--;
continue;
}
if(f < g) {
if(xsub(s1, NSIGNIF-1, 1))
e++;
continue;
}
break;
}
found:
/*
* sign
*/
d = 0;
i = 0;
if(sign)
s2[d++] = '-';
else if(fmt->flags & FmtSign)
s2[d++] = '+';
else if(fmt->flags & FmtSpace)
s2[d++] = ' ';
/*
* copy into final place
* c1 digits of leading '0'
* c2 digits from conversion
* c3 digits of trailing '0'
* c4 digits after '.'
*/
c1 = 0;
c2 = prec + 1;
c3 = 0;
c4 = prec;
switch(chr) {
default:
if(xadd(s1, c2, 5))
e++;
break;
case 'g':
/*
* decide on 'e' of 'f' style convers
*/
if(xadd(s1, c2, 5))
e++;
if(e >= -5 && e <= prec) {
c1 = -e - 1;
c4 = prec - e;
chr = 'h'; // flag for 'f' style
}
break;
case 'f':
if(xadd(s1, c2+e, 5))
e++;
c1 = -e;
if(c1 > prec)
c1 = c2;
c2 += e;
break;
}
/*
* clean up c1 c2 and c3
*/
if(c1 < 0)
c1 = 0;
if(c2 < 0)
c2 = 0;
if(c2 > NSIGNIF) {
c3 = c2-NSIGNIF;
c2 = NSIGNIF;
}
/*
* copy digits
*/
while(c1 > 0) {
if(c1+c2+c3 == c4)
s2[d++] = '.';
s2[d++] = '0';
c1--;
}
while(c2 > 0) {
if(c2+c3 == c4)
s2[d++] = '.';
s2[d++] = s1[i++];
c2--;
}
while(c3 > 0) {
if(c3 == c4)
s2[d++] = '.';
s2[d++] = '0';
c3--;
}
/*
* strip trailing '0' on g conv
*/
if(fmt->flags & FmtSharp) {
if(0 == c4)
s2[d++] = '.';
} else
if(chr == 'g' || chr == 'h') {
for(n=d-1; n>=0; n--)
if(s2[n] != '0')
break;
for(i=n; i>=0; i--)
if(s2[i] == '.') {
d = n;
if(i != n)
d++;
break;
}
}
if(chr == 'e' || chr == 'g') {
if(ucase)
s2[d++] = 'E';
else
s2[d++] = 'e';
c1 = e;
if(c1 < 0) {
s2[d++] = '-';
c1 = -c1;
} else
s2[d++] = '+';
if(c1 >= 100) {
s2[d++] = c1/100 + '0';
c1 = c1%100;
}
s2[d++] = c1/10 + '0';
s2[d++] = c1%10 + '0';
}
s2[d] = 0;
}
int
_floatfmt(Fmt *fmt, double f)
{
char s[FDIGIT+10];
xdtoa(fmt, s, f);
fmt->flags &= FmtWidth|FmtLeft;
_fmtcpy(fmt, s, strlen(s), strlen(s));
return 0;
}
int
_efgfmt(Fmt *f)
{
double d;
d = va_arg(f->args, double);
return _floatfmt(f, d);
}