[Buildroot] [PATCH 2/2] python3: fix double format detection

Jérôme Pouiller jezz at sysmic.org
Wed Nov 9 09:25:08 UTC 2016


Python is not able to detect if compiler double representation is
compliant with IEE754:

  checking whether C doubles are little-endian IEEE 754 binary64... no
  checking whether C doubles are big-endian IEEE 754 binary64... no
  checking whether C doubles are ARM mixed-endian IEEE 754 binary64... no

Accordingly 'legacy' mode isused. It is possible to check this at runtime by
check if 'sys.float_repr_style' contains 'short' or 'legacy'. Calculus
correctness is not garanteed with 'legacy'.

Problem is better described here:

  http://stackoverflow.com/questions/29920294/what-causes-pythons-float-repr-style-to-use-legacy
  https://bugs.python.org/issue7117

However, all gcc architecture use a representation compliant with IEE754. So,
we can enable it unconditionnaly.

Signed-off-by: Jérôme Pouiller <jezz at sysmic.org>
---
 package/python3/python3.mk | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/package/python3/python3.mk b/package/python3/python3.mk
index b3f31c0..cdbe6f0 100644
--- a/package/python3/python3.mk
+++ b/package/python3/python3.mk
@@ -126,6 +126,13 @@ PYTHON3_CONF_ENV += \
 	ac_cv_working_tzset=yes \
 	ac_cv_prog_HAS_HG=/bin/false
 
+# GCC is always compliant with IEEE754
+ifeq ($(call qstrip,$(BR2_ENDIAN)),LITTLE)
+PYTHON3_CONF_ENV += ac_cv_little_endian_double=yes
+else
+PYTHON3_CONF_ENV += ac_cv_big_endian_double=yes
+endif
+
 # uClibc is known to have a broken wcsftime() implementation, so tell
 # Python 3 to fall back to strftime() instead.
 ifeq ($(BR2_TOOLCHAIN_USES_UCLIBC),y)
-- 
2.9.3



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