Fix hypot sNaN handling (bug 20940).

TS 18661-1 generally defines libm functions taking sNaN arguments to
return qNaN and raise "invalid", even for the cases where a
corresponding qNaN argument would not result in a qNaN return.  This
includes hypot with one argument being an infinity and the other being
an sNaN.  This patch duly fixes hypot implementatations in glibc
(generic and powerpc) to ensure qNaN, computed by arithmetic on the
arguments, is returned in that case.

Various implementations do their checks for infinities and NaNs inline
by manipulating the representations of the arguments.  For simplicity,
this patch just uses issignaling to check for sNaN arguments.  This
could be inlined like the existing code (with due care about reversed
quiet NaN conventions, for implementations where that is relevant),
but given that all these checks are in cases where it's already known
at least one argument is not finite, which should be the uncommon
case, that doesn't seem worthwhile unless performance issues are
observed in practice.

Tested for x86_64, x86, mips64 and powerpc.

	[BZ #20940]
	* sysdeps/ieee754/dbl-64/e_hypot.c (__ieee754_hypot): Do not
	return Inf for arguments Inf and sNaN.
	* sysdeps/ieee754/flt-32/e_hypotf.c (__ieee754_hypotf): Likewise.
	* sysdeps/ieee754/ldbl-128/e_hypotl.c (__ieee754_hypotl):
	Likewise.
	* sysdeps/ieee754/ldbl-128ibm/e_hypotl.c (__ieee754_hypotl):
	Likewise.
	* sysdeps/ieee754/ldbl-96/e_hypotl.c (__ieee754_hypotl): Likewise.
	* sysdeps/powerpc/fpu/e_hypot.c (TEST_INF_NAN): Do not return Inf
	for arguments Inf and sNaN.  When returning a NaN, compute it by
	arithmetic on the arguments.
	* sysdeps/powerpc/fpu/e_hypotf.c (TEST_INF_NAN): Likewise.
	* math/libm-test.inc (pow_test_data): Add tests of sNaN arguments.

2 files changed, 12 insertions, 8 deletions

diff --git a/sysdeps/powerpc/fpu/e_hypot.c b/sysdeps/powerpc/fpu/e_hypot.c
index da0f2da..65314c6 100644
--- a/sysdeps/powerpc/fpu/e_hypot.c
+++ b/sysdeps/powerpc/fpu/e_hypot.c
@@ -41,10 +41,11 @@ static const double pdnum   = 2.225073858507201e-308;
 #ifdef _ARCH_PWR7
 /* POWER7 isinf and isnan optimization are fast. */
 # define TEST_INF_NAN(x, y)                                       \
-   if (isinf(x) || isinf(y))                                      \
+   if ((isinf(x) || isinf(y))					  \
+       && !issignaling (x) && !issignaling (y))			  \
        return INFINITY;                                           \
    if (isnan(x) || isnan(y))                                      \
-       return NAN;
+       return x + y;
 # else
 /* For POWER6 and below isinf/isnan triggers LHS and PLT calls are
  * costly (especially for POWER6). */
@@ -66,9 +67,10 @@ static const double pdnum   = 2.225073858507201e-308;
      uint32_t ht = hx; hx = hy; hy = ht;                         \
    }                                                             \
    if (hx >= 0x7ff00000) {                                       \
-     if (hx == 0x7ff00000 || hy == 0x7ff00000)                   \
+     if ((hx == 0x7ff00000 || hy == 0x7ff00000)			 \
+	 && !issignaling (x) && !issignaling (y))		 \
        return INFINITY;                                          \
-     return NAN;                                                 \
+     return x + y;						 \
    }                                                             \
  } while (0)
 
diff --git a/sysdeps/powerpc/fpu/e_hypotf.c b/sysdeps/powerpc/fpu/e_hypotf.c
index 4836082..c182815 100644
--- a/sysdeps/powerpc/fpu/e_hypotf.c
+++ b/sysdeps/powerpc/fpu/e_hypotf.c
@@ -31,10 +31,11 @@
 #ifdef _ARCH_PWR7
 /* POWER7 isinf and isnan optimizations are fast. */
 # define TEST_INF_NAN(x, y)                                      \
-   if (isinff(x) || isinff(y))                                   \
+   if ((isinff(x) || isinff(y))					 \
+       && !issignaling (x) && !issignaling (y))			 \
      return INFINITY;                                            \
    if (isnanf(x) || isnanf(y))                                   \
-     return NAN;
+     return x + y;
 # else
 /* For POWER6 and below isinf/isnan triggers LHS and PLT calls are
  * costly (especially for POWER6). */
@@ -56,9 +57,10 @@
      uint32_t ht = hx; hx = hy; hy = ht;                         \
    }                                                             \
    if (hx >= 0x7f800000) {                                       \
-     if (hx == 0x7f800000 || hy == 0x7f800000)                   \
+     if ((hx == 0x7f800000 || hy == 0x7f800000)			 \
+	 && !issignaling (x) && !issignaling (y))		 \
        return INFINITY;                                          \
-     return NAN;                                                 \
+     return x + y;						 \
    }                                                             \
  } while (0)
 #endif