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optimize more integer cases in floatscan; comment the whole procedure

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This commit is contained in:
Rich Felker 2012-04-12 00:16:01 -04:00
parent 470fecdd3a
commit fe514951af
1 changed files with 27 additions and 8 deletions
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35
src/internal/floatscan.c
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@ -59,12 +59,15 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
int i, j, k, a, z;
long long lrp=-1, dc=0;
long long e10=0;
int lnz = 0;
int gotdig = 0;
int rp;
int e2;
long double y;
long double frac=0;
long double bias=0;
static const int p10s[] = { 10, 100, 1000, 10000,
100000, 1000000, 10000000, 100000000 };
j=0;
k=0;
@ -78,6 +81,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
if (lrp!=-1) break;
lrp = dc;
} else if (k < KMAX-2) {
if (c!='0') lnz = dc;
dc++;
if (j) x[k] = x[k]*10 + c-'0';
else x[k] = c-'0';
@ -114,9 +118,11 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
return 0;
}
if (!x[0])
return sign * 0.0;
if (lrp==dc && (!k || (k==1 && !j)) && (bits>30 || x[0]>>bits==0))
/* Handle zero specially to avoid nasty special cases later */
if (!x[0]) return sign * 0.0;
/* Optimize small integers (w/no exponent) and over/under-flow */
if (lrp==dc && dc<10 && (bits>30 || x[0]>>bits==0))
return sign * (long double)x[0];
if (lrp > -emin/2) {
errno = ERANGE;
@ -127,6 +133,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
return sign * LDBL_MIN * LDBL_MIN;
}
/* Align incomplete final B1B digit */
if (k<KMAX && j) {
for (; j<9; j++) x[k]*=10;
k++;
@ -138,13 +145,19 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
e2 = 0;
rp = lrp;
/* Optimize small to mid-size integers (even in exp. notation) */
if (lnz<9 && lnz<=rp && rp < 18) {
if (rp == 9) return sign * (long double)x[0];
if (rp < 9) return sign * (long double)x[0] / p10s[8-rp];
int bitlim = bits-3*(int)(rp-9);
if (bitlim>30 || x[0]>>bitlim==0)
return sign * (long double)x[0] * p10s[rp-10];
}
/* Align radix point to B1B digit boundary */
if (rp % 9) {
static const int p10s[] = {
100000000, 10000000, 1000000, 100000,
10000, 1000, 100, 10
};
int rpm9 = rp>=0 ? rp%9 : rp%9+9;
int p10 = p10s[rpm9-1];
int p10 = p10s[8-rpm9];
uint32_t carry = 0;
for (k=a; k!=z; k++) {
uint32_t tmp = x[k] % p10;
@ -159,6 +172,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
rp += 9-rpm9;
}
/* Upscale until desired number of bits are left of radix point */
while (rp < 9*LD_B1B_DIG || (rp == 9*LD_B1B_DIG && x[a]<th[0])) {
uint32_t carry = 0;
e2 -= 29;
@ -185,6 +199,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
}
}
/* Downscale until exactly number of bits are left of radix point */
for (;;) {
uint32_t carry = 0;
int sh = 1;
@ -218,6 +233,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
}
}
/* Assemble desired bits into floating point variable */
for (y=i=0; i<LD_B1B_DIG; i++) {
if ((a+i & MASK)==z) x[z=(z+1 & MASK)] = 0;
y = 1000000000.0L * y + x[a+i & MASK];
@ -225,11 +241,13 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
y *= sign;
/* Limit precision for denormal results */
if (bits > LDBL_MANT_DIG+e2-emin) {
bits = LDBL_MANT_DIG+e2-emin;
if (bits<0) bits=0;
}
/* Calculate bias term to force rounding, move out lower bits */
if (bits < LDBL_MANT_DIG) {
bias = copysignl(scalbn(1, 2*LDBL_MANT_DIG-bits-1), y);
frac = fmodl(y, scalbn(1, LDBL_MANT_DIG-bits));
@ -237,6 +255,7 @@ static long double decfloat(FILE *f, int c, int bits, int emin, int sign, int po
y += bias;
}
/* Process tail of decimal input so it can affect rounding */
if ((a+i & MASK) != z) {
uint32_t t = x[a+i & MASK];
if (t < 500000000 && (t || (a+i+1 & MASK) != z))