math: use double_t for temporaries to avoid stores on i386

When FLT_EVAL_METHOD!=0 (only i386 with x87 fp) the excess
precision of an expression must be removed in an assignment.
(gcc needs -fexcess-precision=standard or -std=c99 for this)

This is done by extra load/store instructions which adds code
bloat when lot of temporaries are used and it makes the result
less precise in many cases.
Using double_t and float_t avoids these issues on i386 and
it makes no difference on other archs.

For now only a few functions are modified where the excess
precision is clearly beneficial (mostly polynomial evaluations
with temporaries).

object size differences on i386, gcc-4.8:
             old   new
__cosdf.o    123    95
__cos.o      199   169
__sindf.o    131    95
__sin.o      225   203
__tandf.o    207   151
__tan.o      605   499
erff.o      1470  1416
erf.o       1703  1649
j0f.o       1779  1745
j0.o        2308  2274
j1f.o       1602  1568
j1.o        2286  2252
tgamma.o    1431  1424
math/*.o   64164 63635

1 files changed, 1 insertions, 1 deletions

diff --git a/src/math/__log1pf.h b/src/math/__log1pf.h
index 99492c5a..f2fbef29 100644
--- a/src/math/__log1pf.h
+++ b/src/math/__log1pf.h
@@ -22,7 +22,7 @@ Lg4 = 0xf89e26.0p-26; /* 0.24279078841 */
 
 static inline float __log1pf(float f)
 {
-	float hfsq,s,z,R,w,t1,t2;
+	float_t hfsq,s,z,R,w,t1,t2;
 
 	s = f/(2.0f + f);
 	z = s*s;