gh-145633: remove support for ancient ARM platforms with mixed-endian doubles

Doc/c-api/float.rst

@@ -224,11 +224,6 @@ endian processor, or ``0`` on little endian processor.
 Return value: ``0`` if all is OK, ``-1`` if error (and an exception is set,
 most likely :exc:`OverflowError`).
 
-There are two problems on non-IEEE platforms:
-
-* What this does is undefined if *x* is a NaN or infinity.
-* ``-0.0`` and ``+0.0`` produce the same bytes string.
-
 .. c:function:: int PyFloat_Pack2(double x, char *p, int le)
 
    Pack a C double as the IEEE 754 binary16 half-precision format.
@@ -256,9 +251,6 @@ Return value: The unpacked double.  On error, this is ``-1.0`` and
 :c:func:`PyErr_Occurred` is true (and an exception is set, most likely
 :exc:`OverflowError`).
 
-Note that on a non-IEEE platform this will refuse to unpack a bytes string that
-represents a NaN or infinity.
-
 .. c:function:: double PyFloat_Unpack2(const char *p, int le)
 
    Unpack the IEEE 754 binary16 half-precision format as a C double.

Include/internal/pycore_pymath.h

@@ -182,8 +182,7 @@ extern void _Py_set_387controlword(unsigned short);
 //     (extended precision), and we don't know how to change
 //     the rounding precision.
 #if !defined(DOUBLE_IS_LITTLE_ENDIAN_IEEE754) && \
-    !defined(DOUBLE_IS_BIG_ENDIAN_IEEE754) && \
-    !defined(DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754)
+    !defined(DOUBLE_IS_BIG_ENDIAN_IEEE754)
 #  define _PY_SHORT_FLOAT_REPR 0
 #endif
 

Include/pymacconfig.h

@@ -18,7 +18,6 @@
 #undef SIZEOF_UINTPTR_T
 #undef SIZEOF_PTHREAD_T
 #undef WORDS_BIGENDIAN
-#undef DOUBLE_IS_ARM_MIXED_ENDIAN_IEEE754
 #undef DOUBLE_IS_BIG_ENDIAN_IEEE754
 #undef DOUBLE_IS_LITTLE_ENDIAN_IEEE754
 #undef HAVE_GCC_ASM_FOR_X87

Misc/NEWS.d/next/Core_and_Builtins/2026-03-08-06-18-26.gh-issue-145633.Ogu-RF.rst

@@ -0,0 +1,2 @@
+Remove support for ancient ARM platforms, using mixed-endian representation
+for doubles.  Patch by Sergey B Kirpichev.