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bpo-31031: Unify duplicate bits_in_digit and bit_length (GH-2866)

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Add _Py_bit_length() to unify duplicate bits_in_digit() and bit_length().
This commit is contained in:
Niklas Fiekas 2020-01-16 15:09:19 +01:00 • committed by Victor Stinner
parent 4691a2f2a2
commit c5b79003f5
4 changed files with 35 additions and 54 deletions
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28
Modules/mathmodule.c
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@ -1441,28 +1441,6 @@ math_fsum(PyObject *module, PyObject *seq)
#undef NUM_PARTIALS
/* Return the smallest integer k such that n < 2**k, or 0 if n == 0.
* Equivalent to floor(lg(x))+1. Also equivalent to: bitwidth_of_type -
* count_leading_zero_bits(x)
*/
/* XXX: This routine does more or less the same thing as
* bits_in_digit() in Objects/longobject.c. Someday it would be nice to
* consolidate them. On BSD, there's a library function called fls()
* that we could use, and GCC provides __builtin_clz().
*/
static unsigned long
bit_length(unsigned long n)
{
unsigned long len = 0;
while (n != 0) {
++len;
n >>= 1;
}
return len;
}
static unsigned long
count_set_bits(unsigned long n)
{
@ -1877,7 +1855,7 @@ factorial_partial_product(unsigned long start, unsigned long stop,
/* find midpoint of range(start, stop), rounded up to next odd number. */
midpoint = (start + num_operands) | 1;
left = factorial_partial_product(start, midpoint,
bit_length(midpoint - 2));
_Py_bit_length(midpoint - 2));
if (left == NULL)
goto error;
right = factorial_partial_product(midpoint, stop, max_bits);
@ -1907,7 +1885,7 @@ factorial_odd_part(unsigned long n)
Py_INCREF(outer);
upper = 3;
for (i = bit_length(n) - 2; i >= 0; i--) {
for (i = _Py_bit_length(n) - 2; i >= 0; i--) {
v = n >> i;
if (v <= 2)
continue;
@ -1917,7 +1895,7 @@ factorial_odd_part(unsigned long n)
/* Here inner is the product of all odd integers j in the range (0,
n/2**(i+1)]. The factorial_partial_product call below gives the
product of all odd integers j in the range (n/2**(i+1), n/2**i]. */
partial = factorial_partial_product(lower, upper, bit_length(upper-2));
partial = factorial_partial_product(lower, upper, _Py_bit_length(upper-2));
/* inner *= partial */
if (partial == NULL)
goto error;