Fix soft-fp extended.h unpacking (GCC bug 77265).

soft-fp unpacking for x86 "extended" fails to clear the implicit
mantissa high bit that is explicit in that format, resulting in
problems for operations that expect this bit to be clear in raw
unpacked values.  Specifically, the code for this format is used only
for conversions to and from TFmode (__float128) in libgcc, where this
issue results in GCC bug 77265, extension of long double infinity to
__float128 wrongly produces a NaN.

This patch fixes this by always masking out the implicit bit on
unpacking, so that the results of unpacking meet the expectations of
the rest of the soft-fp code for a normal IEEE format.

Tested for x86_64 in libgcc in conjunction with a GCC testcase for
this issue (this code isn't used in glibc, only in libgcc).

	* soft-fp/extended.h [_FP_W_TYPE_SIZE < 64] (FP_UNPACK_RAW_E):
	Mask implicit bit out of unpacked value.
	[_FP_W_TYPE_SIZE < 64] (FP_UNPACK_RAW_EP): Likewise.
	[_FP_W_TYPE_SIZE >= 64] (FP_UNPACK_RAW_E): Likewise.
	[_FP_W_TYPE_SIZE >= 64] (FP_UNPACK_RAW_EP): Likewise.

diff --git a/ChangeLog b/ChangeLog
index 86dc10526d186b6a7ac6d5c7100918f8e76f27ee..ae29267c1eae41bac7e7e6fbf61aa21dd6fa51da 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2016-08-16  Joseph Myers  <joseph@codesourcery.com>
 
+       * soft-fp/extended.h [_FP_W_TYPE_SIZE < 64] (FP_UNPACK_RAW_E):
+       Mask implicit bit out of unpacked value.
+       [_FP_W_TYPE_SIZE < 64] (FP_UNPACK_RAW_EP): Likewise.
+       [_FP_W_TYPE_SIZE >= 64] (FP_UNPACK_RAW_E): Likewise.
+       [_FP_W_TYPE_SIZE >= 64] (FP_UNPACK_RAW_EP): Likewise.
+
        * sysdeps/sparc/fpu/fesetexcept.c: New file.
 
        * sysdeps/sh/sh4/fpu/fesetexcept.c: New file.

diff --git a/soft-fp/extended.h b/soft-fp/extended.h
index de534483412ba3b34002cfd88547ad9546bf2aca..7b19e835f7a5f0da0a2a0450837c6fce1e750003 100644 (file)
--- a/soft-fp/extended.h
+++ b/soft-fp/extended.h
@@ -104,6 +104,7 @@ union _FP_UNION_E
       X##_f[3] = 0;                                    \
       X##_f[0] = FP_UNPACK_RAW_E_flo.bits.frac0;       \
       X##_f[1] = FP_UNPACK_RAW_E_flo.bits.frac1;       \
+      X##_f[1] &= ~_FP_IMPLBIT_E;                      \
       X##_e  = FP_UNPACK_RAW_E_flo.bits.exp;           \
       X##_s  = FP_UNPACK_RAW_E_flo.bits.sign;          \
     }                                                  \
@@ -119,6 +120,7 @@ union _FP_UNION_E
       X##_f[3] = 0;                                    \
       X##_f[0] = FP_UNPACK_RAW_EP_flo->bits.frac0;     \
       X##_f[1] = FP_UNPACK_RAW_EP_flo->bits.frac1;     \
+      X##_f[1] &= ~_FP_IMPLBIT_E;                      \
       X##_e  = FP_UNPACK_RAW_EP_flo->bits.exp;         \
       X##_s  = FP_UNPACK_RAW_EP_flo->bits.sign;                \
     }                                                  \
@@ -332,6 +334,7 @@ union _FP_UNION_E
       FP_UNPACK_RAW_E_flo.flt = (val);         \
                                                \
       X##_f0 = FP_UNPACK_RAW_E_flo.bits.frac;  \
+      X##_f0 &= ~_FP_IMPLBIT_E;                        \
       X##_f1 = 0;                              \
       X##_e = FP_UNPACK_RAW_E_flo.bits.exp;    \
       X##_s = FP_UNPACK_RAW_E_flo.bits.sign;   \
@@ -345,6 +348,7 @@ union _FP_UNION_E
        = (union _FP_UNION_E *) (val);          \
                                                \
       X##_f0 = FP_UNPACK_RAW_EP_flo->bits.frac;        \
+      X##_f0 &= ~_FP_IMPLBIT_E;                        \
       X##_f1 = 0;                              \
       X##_e = FP_UNPACK_RAW_EP_flo->bits.exp;  \
       X##_s = FP_UNPACK_RAW_EP_flo->bits.sign; \