diff options
| -rw-r--r-- | Lib/test/test_strtod.py | 2 | ||||
| -rw-r--r-- | Misc/NEWS | 10 | ||||
| -rw-r--r-- | Python/dtoa.c | 56 |
3 files changed, 49 insertions, 19 deletions
diff --git a/Lib/test/test_strtod.py b/Lib/test/test_strtod.py index 7800a73..0c6f59d 100644 --- a/Lib/test/test_strtod.py +++ b/Lib/test/test_strtod.py @@ -258,6 +258,8 @@ class StrtodTests(unittest.TestCase): # issue 7632 bug 5: the following 2 strings convert differently '1000000000000000000000000000000000000000e-16', #'10000000000000000000000000000000000000000e-17', + # issue 7632 bug 8: the following produced 10.0 + '10.900000000000000012345678912345678912345', ] for s in test_strings: self.check_strtod(s) @@ -16,10 +16,12 @@ Core and Builtins methods of bytes, bytearray and unicode objects by using a common implementation based on stringlib's fast search. Patch by Florent Xicluna. -- Issue #7632: Fix a crash in dtoa.c that occurred in debug builds - when parsing certain long numeric strings corresponding to subnormal - values. Also fix a number of bugs in dtoa.c that could lead to - incorrectly rounded results when converting strings to floats. +- Issue #7632: Fix various str -> float conversion bugs present in 2.7 + alpha 2, including: (1) a serious 'wrong output' bug that could + occur for long (> 40 digit) input strings, (2) a crash in dtoa.c + that occurred in debug builds when parsing certain long numeric + strings corresponding to subnormal values, and (3) a number of flaws + that could lead to incorrectly rounded results. - Issue #7319, #7770: Silence DeprecationWarning by default when -3 is not used. diff --git a/Python/dtoa.c b/Python/dtoa.c index 51895c7..77117b9 100644 --- a/Python/dtoa.c +++ b/Python/dtoa.c @@ -1340,7 +1340,7 @@ bigcomp(U *rv, const char *s0, BCinfo *bc) 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; @@ -1349,7 +1349,7 @@ _Py_dg_strtod(const char *s00, char **se) 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 '-': @@ -1388,11 +1388,8 @@ _Py_dg_strtod(const char *s00, char **se) 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++; @@ -1477,6 +1474,32 @@ _Py_dg_strtod(const char *s00, char **se) if (!nd0) nd0 = nd; + + /* Summary of parsing results. The parsing stage gives values + * s0, nd0, nd, e, y and z such that: + * + * - nd >= nd0 >= 1 + * + * - the nd significant digits are in s0[0:nd0] and s0[nd0+1:nd+1] + * (using the usual Python half-open slice notation) + * + * - 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] + * + * - the first significant digit is nonzero + * + * - the last significant digit may or may not be nonzero; (some code + * currently assumes that it's nonzero; this is a bug) + * + * - 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. + */ + k = nd < DBL_DIG + 1 ? nd : DBL_DIG + 1; dval(&rv) = y; if (k > 9) { @@ -1593,15 +1616,18 @@ _Py_dg_strtod(const char *s00, char **se) /* 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 +1637,8 @@ _Py_dg_strtod(const char *s00, char **se) 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); |