ref: 0366f11300521165ff22423514a5d829a1f34912
dir: /sys/src/libc/fmt/fltfmt.c/
#include <u.h> #include <libc.h> #include <ctype.h> #include "fmtdef.h" enum { FDIGIT = 30, FDEFLT = 6, NSIGNIF = 17, NEXP10 = 308, }; 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 '.' */ if(chr == 'g' && prec > 0) /* Significant figures. */ prec--; 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 >= -4 && e <= prec) { c1 = -e; 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[1+NEXP10+1+FDIGIT+1]; /* * The max length of a %f string is * '[+-]'+"max exponent"+'.'+"max precision"+'\0' * which is 341 currently. */ 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); }