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gh-146238: Support half-floats in the array module (#146242) · ljfp/cpython@906aff2 · GitHub

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Commit 906aff2

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pythongh-146238: Support half-floats in the array module (python#146242)
Co-authored-by: Victor Stinner <vstinner@python.org>
1 parent 74a1606 commit 906aff2

5 files changed

Lines changed: 90 additions & 6 deletions

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‎Doc/library/array.rst‎

Lines changed: 15 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -42,13 +42,15 @@ defined:
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+-----------+--------------------+-------------------+-----------------------+-------+
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| ``'Q'`` | unsigned long long | int | 8 | |
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+-----------+--------------------+-------------------+-----------------------+-------+
45+
| ``'e'`` | _Float16 | float | 2 | \(3) |
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+-----------+--------------------+-------------------+-----------------------+-------+
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| ``'f'`` | float | float | 4 | |
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+-----------+--------------------+-------------------+-----------------------+-------+
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| ``'d'`` | double | float | 8 | |
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+-----------+--------------------+-------------------+-----------------------+-------+
49-
| ``'F'`` | float complex | complex | 8 | \(3) |
51+
| ``'F'`` | float complex | complex | 8 | \(4) |
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+-----------+--------------------+-------------------+-----------------------+-------+
51-
| ``'D'`` | double complex | complex | 16 | \(3) |
53+
| ``'D'`` | double complex | complex | 16 | \(4) |
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+-----------+--------------------+-------------------+-----------------------+-------+
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@@ -69,6 +71,15 @@ Notes:
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.. versionadded:: 3.13
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(3)
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The IEEE 754 binary16 "half precision" type was introduced in the 2008
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revision of the `IEEE 754 standard <ieee 754 standard_>`_.
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This type is not widely supported by C compilers. It's available
77+
as :c:expr:`_Float16` type, if the compiler supports the Annex H
78+
of the C23 standard.
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.. versionadded:: next
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(4)
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Complex types (``F`` and ``D``) are available unconditionally,
7384
regardless on support for complex types (the Annex G of the C11 standard)
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by the C compiler.
@@ -304,3 +315,5 @@ Examples::
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305316
`NumPy <https://numpy.org/>`_
306317
The NumPy package defines another array type.
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.. _ieee 754 standard: https://en.wikipedia.org/wiki/IEEE_754-2008_revision

‎Doc/whatsnew/3.15.rst‎

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Original file line numberDiff line numberDiff line change
@@ -642,6 +642,10 @@ array
642642
formatting characters ``'F'`` and ``'D'`` respectively.
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(Contributed by Sergey B Kirpichev in :gh:`146151`.)
644644

645+
* Support half-floats (16-bit IEEE 754 binary interchange format): formatting
646+
character ``'e'``.
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(Contributed by Sergey B Kirpichev in :gh:`146238`.)
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645649

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base64
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------

‎Lib/test/test_array.py‎

Lines changed: 11 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -31,7 +31,7 @@ class ArraySubclassWithKwargs(array.array):
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def __init__(self, typecode, newarg=None):
3232
array.array.__init__(self)
3333

34-
typecodes = 'uwbBhHiIlLfdqQFD'
34+
typecodes = 'uwbBhHiIlLfdqQFDe'
3535

3636
class MiscTest(unittest.TestCase):
3737

@@ -117,8 +117,10 @@ def __index__(self):
117117
IEEE_754_FLOAT_COMPLEX_BE = 23
118118
IEEE_754_DOUBLE_COMPLEX_LE = 24
119119
IEEE_754_DOUBLE_COMPLEX_BE = 25
120+
IEEE_754_FLOAT16_LE = 26
121+
IEEE_754_FLOAT16_BE = 27
120122

121-
MACHINE_FORMAT_CODE_MAX = 25
123+
MACHINE_FORMAT_CODE_MAX = 27
122124

123125

124126
class ArrayReconstructorTest(unittest.TestCase):
@@ -1588,6 +1590,13 @@ def test_byteswap(self):
15881590
self.assertEqual(a, b)
15891591

15901592

1593+
class HalfFloatTest(FPTest, unittest.TestCase):
1594+
example = [-42.0, 0, 42, 1e2, -1e4]
1595+
smallerexample = [-42.0, 0, 42, 1e2, -2e4]
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biggerexample = [-42.0, 0, 42, 1e2, 1e4]
1597+
typecode = 'e'
1598+
minitemsize = 2
1599+
15911600
class FloatTest(FPTest, unittest.TestCase):
15921601
typecode = 'f'
15931602
minitemsize = 4

‎Misc/NEWS.d/next/Library/2026-03-21-10-02-20.gh-issue-146238.2WpMOj.rst‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Support half-floats (type code ``'e'`` of the :mod:`struct` module) in the
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:mod:`array` module. Patch by Sergey B Kirpichev.

‎Modules/arraymodule.c‎

Lines changed: 58 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -119,10 +119,12 @@ enum machine_format_code {
119119
IEEE_754_FLOAT_COMPLEX_LE = 22,
120120
IEEE_754_FLOAT_COMPLEX_BE = 23,
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IEEE_754_DOUBLE_COMPLEX_LE = 24,
122-
IEEE_754_DOUBLE_COMPLEX_BE = 25
122+
IEEE_754_DOUBLE_COMPLEX_BE = 25,
123+
IEEE_754_FLOAT16_LE = 26,
124+
IEEE_754_FLOAT16_BE = 27
123125
};
124126
#define MACHINE_FORMAT_CODE_MIN 0
125-
#define MACHINE_FORMAT_CODE_MAX 25
127+
#define MACHINE_FORMAT_CODE_MAX 27
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127129

128130
/*
@@ -611,6 +613,32 @@ QQ_setitem(arrayobject *ap, Py_ssize_t i, PyObject *v)
611613
return 0;
612614
}
613615

616+
static PyObject *
617+
e_getitem(arrayobject *ap, Py_ssize_t i)
618+
{
619+
double x = PyFloat_Unpack2(ap->ob_item + sizeof(short)*i,
620+
PY_LITTLE_ENDIAN);
621+
622+
return PyFloat_FromDouble(x);
623+
}
624+
625+
static int
626+
e_setitem(arrayobject *ap, Py_ssize_t i, PyObject *v)
627+
{
628+
float x;
629+
if (!PyArg_Parse(v, "f;array item must be float", &x)) {
630+
return -1;
631+
}
632+
633+
CHECK_ARRAY_BOUNDS(ap, i);
634+
635+
if (i >= 0) {
636+
return PyFloat_Pack2(x, ap->ob_item + sizeof(short)*i,
637+
PY_LITTLE_ENDIAN);
638+
}
639+
return 0;
640+
}
641+
614642
static PyObject *
615643
f_getitem(arrayobject *ap, Py_ssize_t i)
616644
{
@@ -751,6 +779,7 @@ static const struct arraydescr descriptors[] = {
751779
{'L', sizeof(long), LL_getitem, LL_setitem, LL_compareitems, "L", 1, 0},
752780
{'q', sizeof(long long), q_getitem, q_setitem, q_compareitems, "q", 1, 1},
753781
{'Q', sizeof(long long), QQ_getitem, QQ_setitem, QQ_compareitems, "Q", 1, 0},
782+
{'e', sizeof(short), e_getitem, e_setitem, NULL, "e", 0, 0},
754783
{'f', sizeof(float), f_getitem, f_setitem, NULL, "f", 0, 0},
755784
{'d', sizeof(double), d_getitem, d_setitem, NULL, "d", 0, 0},
756785
{'F', 2*sizeof(float), cf_getitem, cf_setitem, NULL, "F", 0, 0},
@@ -2090,6 +2119,8 @@ static const struct mformatdescr {
20902119
{8, 0, 1}, /* 23: IEEE_754_FLOAT_COMPLEX_BE */
20912120
{16, 0, 0}, /* 24: IEEE_754_DOUBLE_COMPLEX_LE */
20922121
{16, 0, 1}, /* 25: IEEE_754_DOUBLE_COMPLEX_BE */
2122+
{2, 0, 0}, /* 26: IEEE_754_FLOAT16_LE */
2123+
{2, 0, 1} /* 27: IEEE_754_FLOAT16_BE */
20932124
};
20942125

20952126

@@ -2124,6 +2155,9 @@ typecode_to_mformat_code(char typecode)
21242155
case 'w':
21252156
return UTF32_LE + is_big_endian;
21262157

2158+
case 'e':
2159+
return _PY_FLOAT_BIG_ENDIAN ? IEEE_754_FLOAT16_BE : IEEE_754_FLOAT16_LE;
2160+
21272161
case 'f':
21282162
return _PY_FLOAT_BIG_ENDIAN ? IEEE_754_FLOAT_BE : IEEE_754_FLOAT_LE;
21292163

@@ -2309,6 +2343,27 @@ array__array_reconstructor_impl(PyObject *module, PyTypeObject *arraytype,
23092343
return NULL;
23102344
}
23112345
switch (mformat_code) {
2346+
case IEEE_754_FLOAT16_LE:
2347+
case IEEE_754_FLOAT16_BE: {
2348+
Py_ssize_t i;
2349+
int le = (mformat_code == IEEE_754_FLOAT_LE) ? 1 : 0;
2350+
Py_ssize_t itemcount = Py_SIZE(items) / 2;
2351+
const char *memstr = PyBytes_AS_STRING(items);
2352+
2353+
converted_items = PyList_New(itemcount);
2354+
if (converted_items == NULL)
2355+
return NULL;
2356+
for (i = 0; i < itemcount; i++) {
2357+
PyObject *pyfloat = PyFloat_FromDouble(
2358+
PyFloat_Unpack2(&memstr[i * 2], le));
2359+
if (pyfloat == NULL) {
2360+
Py_DECREF(converted_items);
2361+
return NULL;
2362+
}
2363+
PyList_SET_ITEM(converted_items, i, pyfloat);
2364+
}
2365+
break;
2366+
}
23122367
case IEEE_754_FLOAT_LE:
23132368
case IEEE_754_FLOAT_BE: {
23142369
Py_ssize_t i;
@@ -3129,6 +3184,7 @@ The following type codes are defined:\n\
31293184
'L' unsigned integer 4\n\
31303185
'q' signed integer 8 (see note)\n\
31313186
'Q' unsigned integer 8 (see note)\n\
3187+
'e' 16-bit IEEE floats 2\n\
31323188
'f' floating-point 4\n\
31333189
'd' floating-point 8\n\
31343190
'F' float complex 8\n\

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