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Commita96ad31

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gh-94906: Support multiple steps in math.nextafter
1 parent1c0a9c5 commita96ad31

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9 files changed

+139
-17
lines changed

9 files changed

+139
-17
lines changed

‎Doc/library/math.rst‎

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -224,9 +224,9 @@ Number-theoretic and representation functions
224224
of *x* and are floats.
225225

226226

227-
..function::nextafter(x, y)
227+
..function::nextafter(x, y, /, *, steps=1)
228228

229-
Return thenextfloating-point value after *x* towards *y*.
229+
Return the floating-point value *steps* steps after *x* towards *y*.
230230

231231
If *x* is equal to *y*, return *y*.
232232

@@ -239,6 +239,9 @@ Number-theoretic and representation functions
239239

240240
See also:func:`math.ulp`.
241241

242+
..versionchanged::3.12
243+
Added the *steps* argument.
244+
242245
..versionadded::3.9
243246

244247
..function::perm(n, k=None)

‎Include/internal/pycore_global_objects_fini_generated.h‎

Lines changed: 1 addition & 0 deletions
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Include/internal/pycore_global_strings.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -657,6 +657,7 @@ struct _Py_global_strings {
657657
STRUCT_FOR_ID(stdin)
658658
STRUCT_FOR_ID(stdout)
659659
STRUCT_FOR_ID(step)
660+
STRUCT_FOR_ID(steps)
660661
STRUCT_FOR_ID(store_name)
661662
STRUCT_FOR_ID(strategy)
662663
STRUCT_FOR_ID(strftime)

‎Include/internal/pycore_runtime_init_generated.h‎

Lines changed: 1 addition & 0 deletions
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Include/internal/pycore_unicodeobject_generated.h‎

Lines changed: 3 additions & 0 deletions
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Lib/test/test_math.py‎

Lines changed: 17 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -2296,11 +2296,20 @@ def test_nextafter(self):
22962296
float.fromhex('0x1.fffffffffffffp-1'))
22972297
self.assertEqual(math.nextafter(1.0,INF),
22982298
float.fromhex('0x1.0000000000001p+0'))
2299+
self.assertEqual(math.nextafter(1.0,-INF,steps=1),
2300+
float.fromhex('0x1.fffffffffffffp-1'))
2301+
self.assertEqual(math.nextafter(1.0,INF,steps=1),
2302+
float.fromhex('0x1.0000000000001p+0'))
2303+
self.assertEqual(math.nextafter(1.0,-INF,steps=3),
2304+
float.fromhex('0x1.ffffffffffffdp-1'))
2305+
self.assertEqual(math.nextafter(1.0,INF,steps=3),
2306+
float.fromhex('0x1.0000000000003p+0'))
22992307

23002308
# x == y: y is returned
2301-
self.assertEqual(math.nextafter(2.0,2.0),2.0)
2302-
self.assertEqualSign(math.nextafter(-0.0,+0.0),+0.0)
2303-
self.assertEqualSign(math.nextafter(+0.0,-0.0),-0.0)
2309+
forstepsinrange(1,5):
2310+
self.assertEqual(math.nextafter(2.0,2.0,steps=steps),2.0)
2311+
self.assertEqualSign(math.nextafter(-0.0,+0.0,steps=steps),+0.0)
2312+
self.assertEqualSign(math.nextafter(+0.0,-0.0,steps=steps),-0.0)
23042313

23052314
# around 0.0
23062315
smallest_subnormal=sys.float_info.min*sys.float_info.epsilon
@@ -2325,6 +2334,11 @@ def test_nextafter(self):
23252334
self.assertIsNaN(math.nextafter(1.0,NAN))
23262335
self.assertIsNaN(math.nextafter(NAN,NAN))
23272336

2337+
self.assertEqual(1.0,math.nextafter(1.0,INF,steps=0))
2338+
withself.assertRaises(ValueError):
2339+
math.nextafter(1.0,INF,steps=-1)
2340+
2341+
23282342
@requires_IEEE_754
23292343
deftest_ulp(self):
23302344
self.assertEqual(math.ulp(1.0),sys.float_info.epsilon)
Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
Support multiple steps in:func:`math.nextafter`. Patch by Shantanu Jain and Matthias Gorgens.

‎Modules/clinic/mathmodule.c.h‎

Lines changed: 45 additions & 8 deletions
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Modules/mathmodule.c‎

Lines changed: 65 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3893,13 +3893,15 @@ math.nextafter
38933893
x: double
38943894
y: double
38953895
/
3896+
*
3897+
steps: int = 1
38963898
3897-
Return thenextfloating-point value after x towards y.
3899+
Return the floating-point value the given number of steps after x towards y.
38983900
[clinic start generated code]*/
38993901

39003902
staticPyObject*
3901-
math_nextafter_impl(PyObject*module,doublex,doubley)
3902-
/*[clinic end generated code: output=750c8266c1c540ce input=02b2d50cd1d9f9b6]*/
3903+
math_nextafter_impl(PyObject*module,doublex,doubley,intsteps)
3904+
/*[clinic end generated code: output=14190eb869199e5a input=a794e7a79768ee25]*/
39033905
{
39043906
#if defined(_AIX)
39053907
if (x==y) {
@@ -3914,7 +3916,66 @@ math_nextafter_impl(PyObject *module, double x, double y)
39143916
returnPyFloat_FromDouble(y);
39153917
}
39163918
#endif
3917-
returnPyFloat_FromDouble(nextafter(x,y));
3919+
// fast path:
3920+
if (steps==1) {
3921+
returnPyFloat_FromDouble(nextafter(x,y));
3922+
}
3923+
if (steps<0) {
3924+
PyErr_SetString(PyExc_ValueError,"steps must be >= 0");
3925+
returnNULL;
3926+
}
3927+
if (steps==0)
3928+
returnPyFloat_FromDouble(x);
3929+
if (Py_IS_NAN(x)||Py_IS_NAN(y))
3930+
returnPyFloat_FromDouble(x+y);
3931+
3932+
uint64_tusteps=steps;
3933+
3934+
unionpun {doublef;uint64_ti;};
3935+
unionpunux= {x},uy= {y};
3936+
if(ux.i==uy.i) {
3937+
returnPyFloat_FromDouble(x);
3938+
}
3939+
3940+
constuint64_tsign_bit=1ULL<<63;
3941+
3942+
uint64_tax=ux.i& ~sign_bit;
3943+
uint64_tay=uy.i& ~sign_bit;
3944+
3945+
// opposite signs
3946+
if (((ux.i ^uy.i)&sign_bit)) {
3947+
if (ax+ay <=usteps) {
3948+
returnPyFloat_FromDouble(uy.f);
3949+
// We can't use <= here, because of +0.0 vs 0.0
3950+
}elseif (ax<usteps) {
3951+
unionpunresult= {.i= (uy.i&sign_bit) | (usteps-ax)};
3952+
returnPyFloat_FromDouble(result.f);
3953+
}else {
3954+
ux.i-=usteps;
3955+
returnPyFloat_FromDouble(ux.f);
3956+
}
3957+
// same sign now.
3958+
// going down:
3959+
}elseif (ax>ay) {
3960+
// going too far:
3961+
// the addition is not UB,
3962+
// because we have an extra bit at the top of ax and usteps.
3963+
if (ax >=ay+usteps) {
3964+
ux.i-=usteps;
3965+
returnPyFloat_FromDouble(ux.f);
3966+
}else {
3967+
returnPyFloat_FromDouble(uy.f);
3968+
}
3969+
}else {// go up in magnitude. same sign.
3970+
// the addition is not UB,
3971+
// because we have an extra bit at the top of ax and usteps.
3972+
if (ax+usteps <=ay) {
3973+
ux.i+=usteps;
3974+
returnPyFloat_FromDouble(ux.f);
3975+
}else {
3976+
returnPyFloat_FromDouble(uy.f);
3977+
}
3978+
}
39183979
}
39193980

39203981

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