ref: 6ebf0a517b195de7f29ebc9ce817a91e5276107d
dir: /libc/strtod.c/
#include <u.h> #include <libc.h> #include "fmtdef.h" static ulong umuldiv(ulong a, ulong b, ulong c) { double d; d = ((double)a * (double)b) / (double)c; if(d >= 4294967295.) d = 4294967295.; return (ulong)d; } /* * This routine will convert to arbitrary precision * floating point entirely in multi-precision fixed. * The answer is the closest floating point number to * the given decimal number. Exactly half way are * rounded ala ieee rules. * Method is to scale input decimal between .500 and .999... * with external power of 2, then binary search for the * closest mantissa to this decimal number. * Nmant is is the required precision. (53 for ieee dp) * Nbits is the max number of bits/word. (must be <= 28) * Prec is calculated - the number of words of fixed mantissa. */ enum { Nbits = 28, /* bits safely represented in a ulong */ Nmant = 53, /* bits of precision required */ Prec = (Nmant+Nbits+1)/Nbits, /* words of Nbits each to represent mantissa */ Sigbit = 1<<(Prec*Nbits-Nmant), /* first significant bit of Prec-th word */ Ndig = 1500, One = (ulong)(1<<Nbits), Half = (ulong)(One>>1), Maxe = 310, Fsign = 1<<0, /* found - */ Fesign = 1<<1, /* found e- */ Fdpoint = 1<<2, /* found . */ S0 = 0, /* _ _S0 +S1 #S2 .S3 */ S1, /* _+ #S2 .S3 */ S2, /* _+# #S2 .S4 eS5 */ S3, /* _+. #S4 */ S4, /* _+#.# #S4 eS5 */ S5, /* _+#.#e +S6 #S7 */ S6, /* _+#.#e+ #S7 */ S7, /* _+#.#e+# #S7 */ }; static int xcmp(char*, char*); static int fpcmp(char*, ulong*); static void frnorm(ulong*); static void divascii(char*, int*, int*, int*); static void mulascii(char*, int*, int*, int*); typedef struct Tab Tab; struct Tab { int bp; int siz; char* cmp; }; #ifndef ERANGE #define ERANGE 12345 #endif double fmtstrtod(const char *as, char **aas) { int na, ex, dp, bp, c, i, flag, state; ulong low[Prec], hig[Prec], mid[Prec]; double d; char *s, a[Ndig]; flag = 0; /* Fsign, Fesign, Fdpoint */ na = 0; /* number of digits of a[] */ dp = 0; /* na of decimal point */ ex = 0; /* exonent */ state = S0; for(s=(char*)as;; s++) { c = *s; if(c >= '0' && c <= '9') { switch(state) { case S0: case S1: case S2: state = S2; break; case S3: case S4: state = S4; break; case S5: case S6: case S7: state = S7; ex = ex*10 + (c-'0'); continue; } if(na == 0 && c == '0') { dp--; continue; } if(na < Ndig-50) a[na++] = c; continue; } switch(c) { case '\t': case '\n': case '\v': case '\f': case '\r': case ' ': if(state == S0) continue; break; case '-': if(state == S0) flag |= Fsign; else flag |= Fesign; case '+': if(state == S0) state = S1; else if(state == S5) state = S6; else break; /* syntax */ continue; case '.': flag |= Fdpoint; dp = na; if(state == S0 || state == S1) { state = S3; continue; } if(state == S2) { state = S4; continue; } break; case 'e': case 'E': if(state == S2 || state == S4) { state = S5; continue; } break; } break; } /* * clean up return char-pointer */ switch(state) { case S0: if(xcmp(s, "nan") == 0) { if(aas != nil) *aas = s+3; goto retnan; } case S1: if(xcmp(s, "infinity") == 0) { if(aas != nil) *aas = s+8; goto retinf; } if(xcmp(s, "inf") == 0) { if(aas != nil) *aas = s+3; goto retinf; } case S3: if(aas != nil) *aas = (char*)as; goto ret0; /* no digits found */ case S6: s--; /* back over +- */ case S5: s--; /* back over e */ break; } if(aas != nil) *aas = s; if(flag & Fdpoint) while(na > 0 && a[na-1] == '0') na--; if(na == 0) goto ret0; /* zero */ a[na] = 0; if(!(flag & Fdpoint)) dp = na; if(flag & Fesign) ex = -ex; dp += ex; if(dp < -Maxe){ errno = ERANGE; goto ret0; /* underflow by exp */ } else if(dp > +Maxe) goto retinf; /* overflow by exp */ /* * normalize the decimal ascii number * to range .[5-9][0-9]* e0 */ bp = 0; /* binary exponent */ while(dp > 0) divascii(a, &na, &dp, &bp); while(dp < 0 || a[0] < '5') mulascii(a, &na, &dp, &bp); /* close approx by naive conversion */ mid[0] = 0; mid[1] = 1; for(i=0; (c=a[i]); i++) { mid[0] = mid[0]*10 + (c-'0'); mid[1] = mid[1]*10; if(i >= 8) break; } low[0] = umuldiv(mid[0], One, mid[1]); hig[0] = umuldiv(mid[0]+1, One, mid[1]); for(i=1; i<Prec; i++) { low[i] = 0; hig[i] = One-1; } /* binary search for closest mantissa */ for(;;) { /* mid = (hig + low) / 2 */ c = 0; for(i=0; i<Prec; i++) { mid[i] = hig[i] + low[i]; if(c) mid[i] += One; c = mid[i] & 1; mid[i] >>= 1; } frnorm(mid); /* compare */ c = fpcmp(a, mid); if(c > 0) { c = 1; for(i=0; i<Prec; i++) if(low[i] != mid[i]) { c = 0; low[i] = mid[i]; } if(c) break; /* between mid and hig */ continue; } if(c < 0) { for(i=0; i<Prec; i++) hig[i] = mid[i]; continue; } /* only hard part is if even/odd roundings wants to go up */ c = mid[Prec-1] & (Sigbit-1); if(c == Sigbit/2 && (mid[Prec-1]&Sigbit) == 0) mid[Prec-1] -= c; break; /* exactly mid */ } /* normal rounding applies */ c = mid[Prec-1] & (Sigbit-1); mid[Prec-1] -= c; if(c >= Sigbit/2) { mid[Prec-1] += Sigbit; frnorm(mid); } goto out; ret0: return 0; retnan: return __NaN(); retinf: /* * Unix strtod requires these. Plan 9 would return Inf(0) or Inf(-1). */ errno = ERANGE; if(flag & Fsign) return -HUGE_VAL; return HUGE_VAL; out: d = 0; for(i=0; i<Prec; i++) d = d*One + mid[i]; if(flag & Fsign) d = -d; d = ldexp(d, bp - Prec*Nbits); if(d == 0){ /* underflow */ errno = ERANGE; } return d; } static void frnorm(ulong *f) { int i, c; c = 0; for(i=Prec-1; i>0; i--) { f[i] += c; c = f[i] >> Nbits; f[i] &= One-1; } f[0] += c; } static int fpcmp(char *a, ulong* f) { ulong tf[Prec]; int i, d, c; for(i=0; i<Prec; i++) tf[i] = f[i]; for(;;) { /* tf *= 10 */ for(i=0; i<Prec; i++) tf[i] = tf[i]*10; frnorm(tf); d = (tf[0] >> Nbits) + '0'; tf[0] &= One-1; /* compare next digit */ c = *a; if(c == 0) { if('0' < d) return -1; if(tf[0] != 0) goto cont; for(i=1; i<Prec; i++) if(tf[i] != 0) goto cont; return 0; } if(c > d) return +1; if(c < d) return -1; a++; cont:; } } static void divby(char *a, int *na, int b) { int n, c; char *p; p = a; n = 0; while(n>>b == 0) { c = *a++; if(c == 0) { while(n) { c = n*10; if(c>>b) break; n = c; } goto xx; } n = n*10 + c-'0'; (*na)--; } for(;;) { c = n>>b; n -= c<<b; *p++ = c + '0'; c = *a++; if(c == 0) break; n = n*10 + c-'0'; } (*na)++; xx: while(n) { n = n*10; c = n>>b; n -= c<<b; *p++ = c + '0'; (*na)++; } *p = 0; } static Tab tab1[] = { 1, 0, "", 3, 1, "7", 6, 2, "63", 9, 3, "511", 13, 4, "8191", 16, 5, "65535", 19, 6, "524287", 23, 7, "8388607", 26, 8, "67108863", 27, 9, "134217727", }; static void divascii(char *a, int *na, int *dp, int *bp) { int b, d; Tab *t; d = *dp; if(d >= (int)(nelem(tab1))) d = (int)(nelem(tab1))-1; t = tab1 + d; b = t->bp; if(memcmp(a, t->cmp, t->siz) > 0) d--; *dp -= d; *bp += b; divby(a, na, b); } static void mulby(char *a, char *p, char *q, int b) { int n, c; n = 0; *p = 0; for(;;) { q--; if(q < a) break; c = *q - '0'; c = (c<<b) + n; n = c/10; c -= n*10; p--; *p = c + '0'; } while(n) { c = n; n = c/10; c -= n*10; p--; *p = c + '0'; } } static Tab tab2[] = { 1, 1, "", /* dp = 0-0 */ 3, 3, "125", 6, 5, "15625", 9, 7, "1953125", 13, 10, "1220703125", 16, 12, "152587890625", 19, 14, "19073486328125", 23, 17, "11920928955078125", 26, 19, "1490116119384765625", 27, 19, "7450580596923828125", /* dp 8-9 */ }; static void mulascii(char *a, int *na, int *dp, int *bp) { char *p; int d, b; Tab *t; d = -*dp; if(d >= (int)(nelem(tab2))) d = (int)(nelem(tab2))-1; t = tab2 + d; b = t->bp; if(memcmp(a, t->cmp, t->siz) < 0) d--; p = a + *na; *bp -= b; *dp += d; *na += d; mulby(a, p+d, p, b); } static int xcmp(char *a, char *b) { int c1, c2; while((c1 = *b++)) { c2 = *a++; if(isupper(c2)) c2 = tolower(c2); if(c1 != c2) return 1; } return 0; }