Merged revisions 77519,77530,77533 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk
........
r77519 | mark.dickinson | 2010-01-16 10:44:00 +0000 (Sat, 16 Jan 2010) | 5 lines
Issue #7632: Fix a serious wrong output bug for string -> float conversion.
Also remove some now unused variables, and add comments clarifying the
possible outputs of the parsing section of _Py_dg_strtod. Thanks
Eric Smith for reviewing.
........
r77530 | mark.dickinson | 2010-01-16 17:57:49 +0000 (Sat, 16 Jan 2010) | 3 lines
Issue #7632: Fix one more case of incorrect rounding for str -> float
conversion (see bug 5 in the issue tracker).
........
r77533 | mark.dickinson | 2010-01-16 18:06:17 +0000 (Sat, 16 Jan 2010) | 1 line
Fix multiple uses of variable 'L' in _Py_dg_strtod, where one use requires an unsigned long and the other a signed long. See also r77421.
........
diff --git a/Python/dtoa.c b/Python/dtoa.c
index 51895c7..9eb8cdb 100644
--- a/Python/dtoa.c
+++ b/Python/dtoa.c
@@ -1340,16 +1340,17 @@
double
_Py_dg_strtod(const char *s00, char **se)
{
- int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, dp0, dp1, dplen, e, e1, error;
+ int bb2, bb5, bbe, bd2, bd5, bbbits, bs2, c, e, e1, error;
int esign, i, j, k, nd, nd0, nf, nz, nz0, sign;
const char *s, *s0, *s1;
double aadj, aadj1;
U aadj2, adj, rv, rv0;
- ULong y, z, L;
+ ULong y, z, abse;
+ Long L;
BCinfo bc;
Bigint *bb, *bb1, *bd, *bd0, *bs, *delta;
- sign = nz0 = nz = dplen = 0;
+ sign = nz0 = nz = 0;
dval(&rv) = 0.;
for(s = s00;;s++) switch(*s) {
case '-':
@@ -1381,18 +1382,11 @@
goto ret;
}
s0 = s;
- y = z = 0;
for(nd = nf = 0; (c = *s) >= '0' && c <= '9'; nd++, s++)
- if (nd < 9)
- y = 10*y + c - '0';
- else if (nd < 16)
- z = 10*z + c - '0';
+ ;
nd0 = nd;
- dp0 = dp1 = s - s0;
if (c == '.') {
c = *++s;
- dp1 = s - s0;
- dplen = 1;
if (!nd) {
for(; c == '0'; c = *++s)
nz++;
@@ -1409,15 +1403,7 @@
nz++;
if (c -= '0') {
nf += nz;
- for(i = 1; i < nz; i++)
- if (nd++ < 9)
- y *= 10;
- else if (nd <= DBL_DIG + 1)
- z *= 10;
- if (nd++ < 9)
- y = 10*y + c;
- else if (nd <= DBL_DIG + 1)
- z = 10*z + c;
+ nd += nz;
nz = 0;
}
}
@@ -1440,17 +1426,17 @@
while(c == '0')
c = *++s;
if (c > '0' && c <= '9') {
- L = c - '0';
+ abse = c - '0';
s1 = s;
while((c = *++s) >= '0' && c <= '9')
- L = 10*L + c - '0';
- if (s - s1 > 8 || L > MAX_ABS_EXP)
+ abse = 10*abse + c - '0';
+ if (s - s1 > 8 || abse > MAX_ABS_EXP)
/* Avoid confusion from exponents
* so large that e might overflow.
*/
e = (int)MAX_ABS_EXP; /* safe for 16 bit ints */
else
- e = (int)L;
+ e = (int)abse;
if (esign)
e = -e;
}
@@ -1468,15 +1454,78 @@
}
goto ret;
}
- bc.e0 = e1 = e -= nf;
+ e -= nf;
+ if (!nd0)
+ nd0 = nd;
+
+ /* strip trailing zeros */
+ for (i = nd; i > 0; ) {
+ /* scan back until we hit a nonzero digit. significant digit 'i'
+ is s0[i] if i < nd0, s0[i+1] if i >= nd0. */
+ --i;
+ if (s0[i < nd0 ? i : i+1] != '0') {
+ ++i;
+ break;
+ }
+ }
+ e += nd - i;
+ nd = i;
+ if (nd0 > nd)
+ nd0 = nd;
/* Now we have nd0 digits, starting at s0, followed by a
* decimal point, followed by nd-nd0 digits. The number we're
* after is the integer represented by those digits times
* 10**e */
- if (!nd0)
- nd0 = nd;
+ bc.e0 = e1 = e;
+
+ /* Summary of parsing results. The parsing stage gives values
+ * s0, nd0, nd, e, sign, where:
+ *
+ * - s0 points to the first significant digit of the input string s00;
+ *
+ * - nd is the total number of significant digits (here, and
+ * below, 'significant digits' means the set of digits of the
+ * significand of the input that remain after ignoring leading
+ * and trailing zeros.
+ *
+ * - nd0 indicates the position of the decimal point (if
+ * present): so the nd significant digits are in s0[0:nd0] and
+ * s0[nd0+1:nd+1] using the usual Python half-open slice
+ * notation. (If nd0 < nd, then s0[nd0] necessarily contains
+ * a '.' character; if nd0 == nd, then it could be anything.)
+ *
+ * - e is the adjusted exponent: the absolute value of the number
+ * represented by the original input string is n * 10**e, where
+ * n is the integer represented by the concatenation of
+ * s0[0:nd0] and s0[nd0+1:nd+1]
+ *
+ * - sign gives the sign of the input: 1 for negative, 0 for positive
+ *
+ * - the first and last significant digits are nonzero
+ */
+
+ /* put first DBL_DIG+1 digits into integer y and z.
+ *
+ * - y contains the value represented by the first min(9, nd)
+ * significant digits
+ *
+ * - if nd > 9, z contains the value represented by significant digits
+ * with indices in [9, min(16, nd)). So y * 10**(min(16, nd) - 9) + z
+ * gives the value represented by the first min(16, nd) sig. digits.
+ */
+
+ y = z = 0;
+ for (i = 0; i < nd; i++) {
+ if (i < 9)
+ y = 10*y + s0[i < nd0 ? i : i+1] - '0';
+ else if (i < DBL_DIG+1)
+ z = 10*z + s0[i < nd0 ? i : i+1] - '0';
+ else
+ break;
+ }
+
k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1;
dval(&rv) = y;
if (k > 9) {
@@ -1593,15 +1642,18 @@
/* ASSERT(STRTOD_DIGLIM >= 18); 18 == one more than the */
/* minimum number of decimal digits to distinguish double values */
/* in IEEE arithmetic. */
- i = j = 18;
- if (i > nd0)
- j += dplen;
- for(;;) {
- if (--j <= dp1 && j >= dp0)
- j = dp0 - 1;
- if (s0[j] != '0')
- break;
+
+ /* Truncate input to 18 significant digits, then discard any trailing
+ zeros on the result by updating nd, nd0, e and y suitably. (There's
+ no need to update z; it's not reused beyond this point.) */
+ for (i = 18; i > 0; ) {
+ /* scan back until we hit a nonzero digit. significant digit 'i'
+ is s0[i] if i < nd0, s0[i+1] if i >= nd0. */
--i;
+ if (s0[i < nd0 ? i : i+1] != '0') {
+ ++i;
+ break;
+ }
}
e += nd - i;
nd = i;
@@ -1611,8 +1663,8 @@
y = 0;
for(i = 0; i < nd0; ++i)
y = 10*y + s0[i] - '0';
- for(j = dp1; i < nd; ++i)
- y = 10*y + s0[j++] - '0';
+ for(; i < nd; ++i)
+ y = 10*y + s0[i+1] - '0';
}
}
bd0 = s2b(s0, nd0, nd, y);