From: Wilco Dijkstra <wilco.dijkstra@arm.com>
Date: Thu, 30 Oct 2025 15:24:53 +0000 (+0000)
Subject: math: Fix pow special case [BZ #33563]
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=0212fc23b0eeb9d32c9d70d37d36a77cb1185abc;p=thirdparty%2Fglibc.git

math: Fix pow special case [BZ #33563]

Fix pow (DBL_MAX, 1.0) to return DBL_MAX when rouding upwards without FMA.
This fixes BZ #33563.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
---

diff --git a/sysdeps/ieee754/dbl-64/e_pow.c b/sysdeps/ieee754/dbl-64/e_pow.c
index 3d6933137c..3dc171885a 100644
--- a/sysdeps/ieee754/dbl-64/e_pow.c
+++ b/sysdeps/ieee754/dbl-64/e_pow.c
@@ -147,8 +147,14 @@ specialcase (double_t tmp, uint64_t sbits, uint64_t ki)
       /* k > 0, the exponent of scale might have overflowed by <= 460.  */
       sbits -= 1009ull << 52;
       scale = asdouble (sbits);
-      y = 0x1p1009 * (scale + scale * tmp);
-      return check_oflow (y);
+      y = scale + scale * tmp;
+#ifndef __FP_FAST_FMA
+      /* Special case pow (0x1.fffffffffffffp+1023, 1.0) when rounding up.  */
+      if (WANT_ROUNDING && y == 0x1p15
+	  && (math_opt_barrier (1.0) + 0x1p-60) != 1.0)
+	return DBL_MAX;
+#endif
+      return check_oflow (y * 0x1p1009);
     }
   /* k < 0, need special care in the subnormal range.  */
   sbits += 1022ull << 52;