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GH-101291: Rearrange the size bits in PyLongObject by markshannon · Pull Request #102464 · python/cpython · GitHub
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GH-101291: Rearrange the size bits in PyLongObject #102464

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Merged
markshannon merged 37 commits into from
Mar 22, 2023
Merged

GH-101291: Rearrange the size bits in PyLongObject #102464

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0ec07e4
Add functions to hide some internals of long object.
markshannon Jan 25, 2023
292b9d0
Add internal functions to longobject.c for setting sign and digit count.
markshannon Jan 25, 2023
5c54894
Replace Py_SIZE(x) < 0 with _PyLong_IsNegative(x) in longobject.c
markshannon Feb 28, 2023
029aaa4
Replace Py_ABS(Py_SIZE(a)) with _PyLong_DigitCount(a) in longobject.c
markshannon Feb 28, 2023
b56e6da
Remove many uses of Py_SIZE in longobject.c
markshannon Feb 28, 2023
91269fc
Remove _PyLong_AssignValue, as it is no longer used.
markshannon Feb 28, 2023
c48e825
Remove some more uses of Py_SIZE in longobject.c.
markshannon Feb 28, 2023
449c0e2
Remove a few more uses of Py_SIZE in longobject.c.
markshannon Mar 1, 2023
c5ba601
Remove some more uses of Py_SIZE, replacing with _PyLong_UnsignedDigi…
markshannon Mar 1, 2023
4b3a3e8
Replace a few Py_SIZE() with _PyLong_SameSign().
markshannon Mar 1, 2023
9ef9d2c
Remove a few more Py_SIZE() from longobject.c
markshannon Mar 1, 2023
9c408c1
Replace uses of IS_MEDIUM_VALUE macro with _PyLong_IsSingleDigit.
markshannon Mar 1, 2023
548d656
Remove most of the remaining uses of Py_SIZE in longobject.c
markshannon Mar 1, 2023
3e3fefd
Replace last remaining uses of Py_SIZE applied to longobject with _Py…
markshannon Mar 1, 2023
391fb51
Don't use _PyObject_InitVar and move a couple of inline functions to …
markshannon Mar 1, 2023
df8c7d3
Correct name of inline function.
markshannon Mar 1, 2023
bc14fa6
Eliminate all remaining uses of Py_SIZE and Py_SET_SIZE on PyLongObject.
markshannon Mar 1, 2023
54c6f1b
Change layout of size/sign bits in longobject to support future addit…
markshannon Mar 2, 2023
ce6bfb2
Test pairs of longs together on fast path of add/mul/sub.
markshannon Mar 2, 2023
4c1956b
Tidy up comment and delete commented out code.
markshannon Mar 6, 2023
301158b
Add news.
markshannon Mar 6, 2023
1aa1891
Remove debugging asserts.
markshannon Mar 6, 2023
bf2a9af
Fix storage classes.
markshannon Mar 6, 2023
169f521
Remove development debug functions.
markshannon Mar 6, 2023
90f9072
Avoid casting to smaller int.
markshannon Mar 8, 2023
f143443
Apply suggestions from code review.
markshannon Mar 8, 2023
a0d661e
Widen types to avoid data loss.
markshannon Mar 8, 2023
145a2e4
Fix syntax error.
markshannon Mar 8, 2023
638a98f
Replace 'SingleDigit' with 'Compact' as the term 'single digit' seems…
markshannon Mar 9, 2023
7f5acc0
Address review comments.
markshannon Mar 16, 2023
b06bb6f
Merge branch 'main' into long-rearrange-size-bits
markshannon Mar 16, 2023
a19b0a7
Merge branch 'main' into long-rearrange-size-bits
markshannon Mar 16, 2023
87f49b2
Fix _PyLong_Sign
markshannon Mar 16, 2023
f764aa8
Replace _PyLong_Sign(x) < 0 with _PyLong_IsNegative(x).
markshannon Mar 16, 2023
9843ac0
fix sign check
markshannon Mar 16, 2023
d6cb917
Address some review comments.
markshannon Mar 22, 2023
469d26f
Change asserts on digit counts to asserts on sign where applicable.
markshannon Mar 22, 2023
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Test pairs of longs together on fast path of add/mul/sub.
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@markshannon
markshannon committed Mar 2, 2023
commit ce6bfb28f624070dc26ae0bbc49b0a753c4481a3
7 changes: 7 additions & 0 deletions Include/internal/pycore_long.h
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Expand Up @@ -150,6 +150,13 @@ _PyLong_IsSingleDigit(const PyLongObject* op) {
return op->long_value.lv_tag < (2 << NON_SIZE_BITS);
}

static inline int
_PyLong_BothAreSingleDigit(const PyLongObject* a, PyLongObject* b) {

@lpereira lpereira Mar 8, 2023

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Suggested change
_PyLong_BothAreSingleDigit(const PyLongObject* a, PyLongObject* b) {
_PyLong_BothAreSingleDigit(const PyLongObject* a, const PyLongObject* b) {

assert(PyLong_Check(a));
assert(PyLong_Check(b));
return (a->long_value.lv_tag | b->long_value.lv_tag) < (2 << NON_SIZE_BITS);
}

static inline Py_ssize_t
_PyLong_SingleDigitValue(const PyLongObject *op)
{
Expand Down
9 changes: 6 additions & 3 deletions Objects/longobject.c
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Expand Up @@ -3216,6 +3216,9 @@ PyLong_AsDouble(PyObject *v)
static Py_ssize_t
long_compare(PyLongObject *a, PyLongObject *b)
{
if (_PyLong_BothAreSingleDigit(a, b)) {
return _PyLong_SingleDigitValue(a) - _PyLong_SingleDigitValue(b);

@lpereira lpereira Mar 8, 2023 •
edited
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This doesn't work well in the case where a is LONG_MAX and b is -1: this will not only result in LONG_MIN (which is wrong in this case, as a is clearly larger than b), this will also cause an overflow, which is undefined for signed integers. Might want to consider using some other method, such as (a > b) - (a < b) or something like that.

@markshannon markshannon Mar 9, 2023

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If the values fit in a "single digit", then they have at least one bit to spare, so that +, - cannot overflow.
I'll add comments to _PyLong_IsSingleDigit and _PyLong_BothAreSingleDigit to make that clear.

}
Py_ssize_t sign = _PyLong_SignedDigitCount(a) - _PyLong_SignedDigitCount(b);
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if (sign == 0) {
Py_ssize_t i = _PyLong_DigitCount(a);
Expand Down Expand Up @@ -3392,7 +3395,7 @@ x_sub(PyLongObject *a, PyLongObject *b)
PyObject *
_PyLong_Add(PyLongObject *a, PyLongObject *b)
{
if (_PyLong_IsSingleDigit(a) && _PyLong_IsSingleDigit(b)) {
if (_PyLong_BothAreSingleDigit(a, b)) {
return _PyLong_FromSTwoDigits(medium_value(a) + medium_value(b));
}

Expand Down Expand Up @@ -3433,7 +3436,7 @@ _PyLong_Subtract(PyLongObject *a, PyLongObject *b)
{
PyLongObject *z;

if (_PyLong_IsSingleDigit(a) && _PyLong_IsSingleDigit(b)) {
if (_PyLong_BothAreSingleDigit(a, b)) {
return _PyLong_FromSTwoDigits(medium_value(a) - medium_value(b));
}
if (_PyLong_IsNegative(a)) {
Expand Down Expand Up @@ -3885,7 +3888,7 @@ _PyLong_Multiply(PyLongObject *a, PyLongObject *b)
PyLongObject *z;

/* fast path for single-digit multiplication */
if (_PyLong_IsSingleDigit(a) && _PyLong_IsSingleDigit(b)) {
if (_PyLong_BothAreSingleDigit(a, b)) {
stwodigits v = medium_value(a) * medium_value(b);
return _PyLong_FromSTwoDigits(v);
}
Expand Down