From: Eric Botcazou <ebotcazou@adacore.com>
Date: Wed, 20 Jan 2021 16:08:51 +0000 (+0100)
Subject: [Ada] Fix off-by-one bug in underflow handling of Scaling
X-Git-Tag: basepoints/gcc-13~7768
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bcc6807c4bbcb782cc0f1453bb9275d52a7e1638;p=thirdparty%2Fgcc.git

[Ada] Fix off-by-one bug in underflow handling of Scaling

gcc/ada/

	* libgnat/s-fatgen.adb (Scaling): Fix off-by-one bug for underflow.
---

diff --git a/gcc/ada/libgnat/s-fatgen.adb b/gcc/ada/libgnat/s-fatgen.adb
index 95c0549e53c6..145d4ac9b0ec 100644
--- a/gcc/ada/libgnat/s-fatgen.adb
+++ b/gcc/ada/libgnat/s-fatgen.adb
@@ -784,7 +784,7 @@ package body System.Fat_Gen is
             --  Check for gradual underflow
 
             if T'Denorm
-              and then Adjustment >= IEEE_Emin - (Mantissa - 1) - Exp
+              and then Adjustment >= IEEE_Emin - Mantissa - Exp
             then
                Expf := IEEE_Emin;
                Expi := Exp + Adjustment - Expf;
@@ -807,6 +807,13 @@ package body System.Fat_Gen is
                         Float_Word (IEEE_Ebias + Expf) * Exp_Factor;
 
          if Expi < 0 then
+            --  Given that Expi >= -Mantissa, only -64 is problematic
+
+            if Expi = -64 then
+               XX := XX / 2.0;
+               Expi := -63;
+            end if;
+
             XX := XX / T (UST.Long_Long_Unsigned (2) ** (-Expi));
          end if;