diff options
Diffstat (limited to 'Objects/longobject.c')
| -rw-r--r-- | Objects/longobject.c | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/Objects/longobject.c b/Objects/longobject.c index fab7dee..6dedd38 100644 --- a/Objects/longobject.c +++ b/Objects/longobject.c @@ -1556,7 +1556,7 @@ x_mul(PyLongObject *a, PyLongObject *b) carry >>= SHIFT; } } - return z; + return long_normalize(z); } /* A helper for Karatsuba multiplication (k_mul). @@ -1630,8 +1630,15 @@ k_mul(PyLongObject *a, PyLongObject *b) } /* Use gradeschool math when either number is too small. */ - if (ABS(a->ob_size) <= KARATSUBA_CUTOFF) - return x_mul(a, b); + if (ABS(a->ob_size) <= KARATSUBA_CUTOFF) { + /* 0 is inevitable if one kmul arg has more than twice + * the digits of another, so it's worth special-casing. + */ + if (a->ob_size == 0) + return _PyLong_New(0); + else + return x_mul(a, b); + } shift = ABS(b->ob_size) >> 1; if (kmul_split(a, shift, &ah, &al) < 0) goto fail; @@ -1641,16 +1648,21 @@ k_mul(PyLongObject *a, PyLongObject *b) assert(ahbh->ob_size >= 0); /* Allocate result space, and copy ahbh into the high digits. */ - ret = _PyLong_New(ahbh->ob_size + 2*shift + 1); + ret = _PyLong_New(ABS(a->ob_size) + ABS(b->ob_size)); if (ret == NULL) goto fail; #ifdef Py_DEBUG /* Fill with trash, to catch reference to uninitialized digits. */ memset(ret->ob_digit, 0xDF, ret->ob_size * sizeof(digit)); #endif + assert(2*shift + ahbh->ob_size <= ret->ob_size); memcpy(ret->ob_digit + 2*shift, ahbh->ob_digit, ahbh->ob_size * sizeof(digit)); - /* That didn't copy into the most-significant (overflow) digit. */ - ret->ob_digit[ret->ob_size - 1] = 0; + + /* Zero-out the digits higher than the ahbh copy. */ + i = ret->ob_size - 2*shift - ahbh->ob_size; + if (i) + memset(ret->ob_digit + 2*shift + ahbh->ob_size, 0, + i * sizeof(digit)); /* Compute al*bl, and copy into the low digits. */ if ((albl = k_mul(al, bl)) == NULL) goto fail; |