[Qemu-devel] [PATCH 00/20] target-i386 conversion to softfloat

[Aurelien Jarno]

The i386 target is the last one still using softfloat-native. Compared 
to softfloat, it is faster but lacks exception handling, float80 
(except on x86 hosts) and float128, as well as correctness (use NaN 
propagation from the host, different corner cases, etc.). It's API has
also diverged from softfloat, meaning it's not easily possible to select
softfloat or softfloat-native at build-time.

This patch series adjust softfloat, softfloat-native, and target-i386,
so that it's possible to build this target with either implementation.
It's only a transient state until softfloat-native is definitely 
removed. This also mean that some code changes in target-i386 are not
the best possible, as writing code that work on both is sometimes 
difficult. This will have to be fixed after the softfloat removal.

For the trigonometic and logarithmic functions, which are not (yet)
available in softfloat (neither in softfloat-native actually), I have
chosen to convert the floatx80 value to double and use the host 
function. This limits the precision to float64, but anyway the current
code was already using the double version of these functions (instead
of the long double version for floatx80 precision).

I have tested these patches by using the GNU libc testsuite, and 
comparing the results before and after. This patch series already 
globally improve the testsuite results, though on some trigonometric 
functions some tests are now failing and some tests are now passing,
due to precision issues. In any case, these precision issues are limited
to the last two bits of the 80-bit value, so it's safe to ignore this
issue for now.

I already have another patch series in preparation, which does the 
actual softfloat removal, clean the generic and target-i386 codes, add 
exception support, and add a softfloat log2() function. However it's
the following step, and I prefer first to get this patch series 
discussed and hopefully accepted before.


Aurelien Jarno (20):
  softfloat: fix floatx80 handling of NaN
  softfloat: fix floatx80_is_infinity()
  softfloat: add floatx80 constants
  softfloat: add pi constants
  softfloat-native: add a few constant values
  softfloat: add floatx80_compare*() functions
  softfloat: fix float*_scalnb() corner cases
  softfloat-native: fix float*_scalbn() functions
  softfloat-native: add float*_is_any_nan() functions
  target-i386: fix helper_fscale() wrt softfloat
  target-i386: fix helper_flbd_ST0() wrt softfloat
  target-i386: fix helper_fxtract() wrt softfloat
  target-i386: fix helper_fdiv() wrt softfloat
  target-i386: fix helper_fsqrt() wrt softfloat
  target-i386: replace approx_rsqrt and approx_rcp by softfloat ops
  target-i386: add CPU86_LDouble <-> double conversion functions
  target-i386: fix logarithmic and trigonometric helpers wrt softfloat
  target-i386: fix helper_fprem() and helper_fprem1() wrt softfloat
  target-i386: fix constants wrt softfloat
  target-i386: switch to softfloat

 configure                  |    3 -
 fpu/softfloat-native.c     |   26 ++++++
 fpu/softfloat-native.h     |   36 +++++++-
 fpu/softfloat-specialize.h |   19 +++--
 fpu/softfloat.c            |   93 +++++++++++++++++++-
 fpu/softfloat.h            |   14 +++-
 target-i386/exec.h         |   20 +++++
 target-i386/op_helper.c    |  205 ++++++++++++++++++++++++++-----------------
 target-i386/ops_sse.h      |   36 +++++---
 9 files changed, 341 insertions(+), 111 deletions(-)

-- 
1.7.2.3