optimize more integer cases in floatscan; comment the whole procedure

[musl] / src / internal / floatscan.c

diff --git a/src/internal/floatscan.c b/src/internal/floatscan.c
index 28a09c2..0e1f6d0 100644 (file)
--- a/src/internal/floatscan.c
+++ b/src/internal/floatscan.c
@@ -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))