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* bignum.c (big2dbl): more precise conversion at edge cases.

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[ruby-dev:34195]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15881 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
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nobu 2008-04-01 07:40:23 +00:00
parent 05da1ec22d
commit e31a69562e
2 changed files with 58 additions and 4 deletions
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5
ChangeLog
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@ -1,3 +1,8 @@
Tue Apr 1 16:40:21 2008 Nobuyoshi Nakada <nobu@ruby-lang.org>
* bignum.c (big2dbl): more precise conversion at edge cases.
[ruby-dev:34195]
Tue Apr 1 14:43:38 2008 Nobuyoshi Nakada <nobu@ruby-lang.org>
* configure.in: get rid of empty expansion.

55
bignum.c
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@ -1133,16 +1133,65 @@ rb_dbl2big(double d)
return bignorm(dbl2big(d));
}
static int
nlz(BDIGIT x)
{
BDIGIT y;
int n = BITSPERDIG;
#if BITSPERDIG > 64
y = x >> 64; if (y) {n -= 64; x = y;}
#endif
#if BITSPERDIG > 32
y = x >> 32; if (y) {n -= 32; x = y;}
#endif
#if BITSPERDIG > 16
y = x >> 16; if (y) {n -= 16; x = y;}
#endif
y = x >> 8; if (y) {n -= 8; x = y;}
y = x >> 4; if (y) {n -= 4; x = y;}
y = x >> 2; if (y) {n -= 2; x = y;}
y = x >> 1; if (y) {return n - 2;}
return n - x;
}
static double
big2dbl(VALUE x)
{
double d = 0.0;
long i = RBIGNUM_LEN(x);
BDIGIT *ds = BDIGITS(x);
long i = RBIGNUM_LEN(x), lo = 0, bits;
BDIGIT *ds = BDIGITS(x), dl;
while (i--) {
if (i) {
bits = i * BITSPERDIG - nlz(ds[i-1]);
if (bits > DBL_MANT_DIG+DBL_MAX_EXP) {
d = HUGE_VAL;
}
else {
if (bits > DBL_MANT_DIG+1)
lo = (bits -= DBL_MANT_DIG+1) / BITSPERDIG;
else
bits = 0;
while (--i > lo) {
d = ds[i] + BIGRAD*d;
}
dl = ds[i];
if (bits && (dl & (1UL << (bits %= BITSPERDIG)))) {
int carry = dl & ~(~0UL << bits);
if (!carry) {
while (i-- > 0) {
if ((carry = ds[i]) != 0) break;
}
}
if (carry) {
dl &= ~0UL << bits;
dl += 1UL << bits;
if (!dl) d += 1;
}
}
d = dl + BIGRAD*d;
if (lo) d = ldexp(d, lo * BITSPERDIG);
}
}
if (!RBIGNUM_SIGN(x)) d = -d;
return d;
}