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=f186365aee5a894e3cc26fa64af573e264c38ff6'>root</a>/<a href='/guix/log/tests?id=f186365aee5a894e3cc26fa64af573e264c38ff6'>tests</a>/<a href='/guix/log/tests/guix-git-authenticate.sh?id=f186365aee5a894e3cc26fa64af573e264c38ff6'>guix-git-authenticate.sh</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/tests/guix-git-authenticate.sh?id=f186365aee5a894e3cc26fa64af573e264c38ff6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-09-28 21:06:36 -0500'>2020-09-28</span></td><td><a href='/guix/commit/tests/guix-git-authenticate.sh?id=d8934360d2453a403b5433e71d09188e4ed23b57'>tests: Simplify shell exit status negation;</a><span class='msg-avail'>...<span class='msg-tooltip'>* tests/guix-archive.sh, tests/guix-build-branch.sh, tests/guix-build.sh,
tests/guix-daemon.sh, tests/guix-download.sh, tests/guix-environment.sh,
tests/guix-gc.sh, tests/guix-git-authenticate.sh, tests/guix-graph.sh,
tests/guix-hash.sh, tests/guix-lint.sh, tests/guix-pack-relocatable.sh,
tests/guix-pack.sh, tests/guix-package-aliases.sh, tests/guix-package-net.sh,
tests/guix-package.sh: Use the shell '!' keyword to negate command exit status
in place of 'if ...; then false; else true; fi'
</span></span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2020-07-11 12:33:01 +0200'>2020-07-11</span></td><td><a href='/guix/commit/tests/guix-git-authenticate.sh?id=a98712785e0b042a290420fd74e5a4a5da4fc68f'>Add 'guix git authenticate'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/git.scm, guix/scripts/git/authenticate.scm,
tests/guix-git-authenticate.sh: New files.
* Makefile.am (MODULES): Add the *.scm files.
(SH_TESTS): Add 'tests/guix-git-authenticate.sh'.
* doc/guix.texi (Channels)[Specifying Channel Authorizations]: Mention
'guix git authenticate'.
(Invoking guix git authenticate): New node.
* po/guix/POTFILES.in: Add 'guix/scripts/git.scm' and
'guix/scripts/git/authenticate.scm'.
</span></span></td><td>Ludovic Courtès</td></tr>