Copied from Debian.

From: Dave Martin
Subject: "rsc" doesnt exist anymore in thumb2

diff --git a/fixed.h b/fixed.h
index 4b58abf..ba4bc26 100644
--- a/fixed.h
+++ b/fixed.h
@@ -275,12 +275,25 @@ mad_fixed_t mad_f_mul_inline(mad_fixed_t x, mad_fixed_t y)
 	 : "+r" (lo), "+r" (hi)  \
 	 : "%r" (x), "r" (y))
 
+#ifdef __thumb__
+/* In Thumb-2, the RSB-immediate instruction is only allowed with a zero
+	operand.  If needed this code can also support Thumb-1 
+	(simply append "s" to the end of the second two instructions). */
+#  define MAD_F_MLN(hi, lo)  \
+    asm ("rsbs        %0, %0, #0\n\t"  \
+	 "sbc   %1, %1, %1\n\t"  \
+	 "sub   %1, %1, %2"  \
+	 : "+&r" (lo), "=&r" (hi)  \
+	 : "r" (hi)  \
+	 : "cc")
+#else /* ! __thumb__ */
 #  define MAD_F_MLN(hi, lo)  \
     asm ("rsbs	%0, %2, #0\n\t"  \
 	 "rsc	%1, %3, #0"  \
-	 : "=r" (lo), "=r" (hi)  \
+	 : "=&r" (lo), "=r" (hi)  \
 	 : "0" (lo), "1" (hi)  \
 	 : "cc")
+#endif /* __thumb__ */
 
 #  define mad_f_scale64(hi, lo)  \
     ({ mad_fixed_t __result;  \
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<div class='path'>path: <a href='/guix/log/?id=f185f81c72179209edc9c6eee0e554855dda87a5'>root</a>/<a href='/guix/log/doc?id=f185f81c72179209edc9c6eee0e554855dda87a5'>doc</a>/<a href='/guix/log/doc/htmlxref.cnf?id=f185f81c72179209edc9c6eee0e554855dda87a5'>htmlxref.cnf</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/doc/htmlxref.cnf?id=f185f81c72179209edc9c6eee0e554855dda87a5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-12-18 16:01:32 +0100'>2022-12-18</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=8e2f32cee982d42a79e53fc1e9aa7b8ff0514714'>doc: Update URLs for the manual and cookbook translations.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf: Update URLs for "guix" and "guix-cookbook".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-12-18 15:53:43 +0100'>2022-12-18</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=b77b4c7c3a5ac180f5aed0983be50ffbe6832f87'>doc: Add guile-netlink to 'htmlxref.cnf'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf: Add guile-netlink.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-08-05 00:14:29 +0200'>2022-08-05</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=f9a267c6d266355b48bd12288f4414eaf4db8b33'>doc: Fix Guix manual URLs in 'htmlxref.cnf'.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes a regression introduced in
868da34d54365023223a4ff7520043ba55ad64e8.

* doc/htmlxref.cnf (GUIX): Remove "/guix".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-06-16 21:52:49 -0400'>2022-06-16</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=ec7a75034421654d2ece2ba20033b44d345547f0'>doc: Remove obsolete comment from htmlxref.cnf.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is follow up to &lt;https://issues.guix.gnu.org/55290&gt;.

* doc/htmlxref.cnf (geiser): Delete obsolete comment.
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-04-08 19:59:25 +0200'>2022-04-08</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=868da34d54365023223a4ff7520043ba55ad64e8'>doc: Fix cookbook URLs in htmlxref.cnf.</a><span class='msg-avail'>...<span class='msg-tooltip'>Reported by Greg Hogan &lt;code@greghogan.com&gt;.

* doc/htmlxref.cnf (GUIX_ROOT): New variable.
(GUIX, GUIX_COOKBOOK): Adjust.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-10-04 16:36:58 +0200'>2021-10-04</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=1267c2e9efdb6e324ce1c7b1fcef242f8208a61f'>doc: Update htmlxref.cnf.</a><span class='msg-avail'>...<span class='msg-tooltip'>Update and fix broken references to cuirass, git, and guix-cookbook.

* doc/htmlxref.cnf: Update from Texinfo.  Factorize Guix manuals.
(cuirass, git, guix-cookbook, guix-cookbook.de, guix-cookbook.fr): New
entries.

Signed-off-by: Ludovic Courtès &lt;ludo@gnu.org&gt;
</span></span></td><td>Sarah Morgensen</td></tr>
<tr><td><span title='2021-04-24 16:46:22 +0200'>2021-04-24</span></td><td><a href='/guix/commit/doc/htmlxref.cnf?id=1ebd086286c3825cfae31e75f8394986f1a18736'>doc: Fix cross-reference URL to translated manual.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/htmlxref.cnf: Fix translated manual URL.
</span></span></td><td>Julien Lepiller</td></tr>