python · skirpichev · Mar 7, 2026 · Mar 8, 2026 · Mar 8, 2026 · Mar 9, 2026
@@ -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.

diff --git a/Include/internal/pycore_pymath.h b/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
 

@@ -13,7 +13,7 @@ extern "C" {
 #include "pycore_debug_offsets.h"  // _Py_DebugOffsets_INIT()
 #include "pycore_dtoa.h"          // _dtoa_state_INIT()
 #include "pycore_faulthandler.h"  // _faulthandler_runtime_state_INIT
-#include "pycore_floatobject.h"   // _py_float_format_unknown
+#include "pycore_floatobject.h"   // _py_float_format_*
 #include "pycore_function.h"
 #include "pycore_hamt.h"          // _PyHamt_BitmapNode_Type
 #include "pycore_import.h"        // IMPORTS_INIT
@@ -85,8 +85,8 @@ extern PyTypeObject _PyExc_MemoryError;
             .is_global = 1, \
         }, \
         .float_state = { \
-            .float_format = _py_float_format_unknown, \
-            .double_format = _py_float_format_unknown, \
+            .float_format = _py_float_format_ieee_little_endian, \
+            .double_format = _py_float_format_ieee_little_endian, \
         }, \
         .types = { \
             .next_version_tag = _Py_TYPE_VERSION_NEXT, \
@@ -233,4 +233,4 @@ extern PyTypeObject _PyExc_MemoryError;
 #ifdef __cplusplus
 }
 #endif
-#endif /* !Py_INTERNAL_RUNTIME_INIT_H */
+#endif /* !Py_INTERNAL_RUNTIME_INIT_H */
diff --git a/Include/internal/pycore_runtime_structs.h b/Include/internal/pycore_runtime_structs.h
@@ -36,7 +36,6 @@ struct _pymem_allocators {
 };
 
 enum _py_float_format_type {
-    _py_float_format_unknown,
     _py_float_format_ieee_big_endian,
     _py_float_format_ieee_little_endian,
 };

diff --git a/Include/pymacconfig.h b/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

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-03-08-06-18-26.gh-issue-145633.Ogu-RF.rst b/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.
diff --git a/Objects/clinic/floatobject.c.h b/Objects/clinic/floatobject.c.h
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Remove support for ancient ARM platforms, using mixed-endian representation
		for doubles. Patch by Sergey B Kirpichev.
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