1From 09e21bb5d6714687705dc8f2d00a09b3ff3b2436 Mon Sep 17 00:00:00 2001
 2From: Michael Forney <mforney@mforney.org>
 3Date: Fri, 7 Jun 2019 11:55:26 -0700
 4Subject: [PATCH] Avoid __builtin_ffs
 5
 6---
 7 src/common.h | 5 +----
 8 src/core.c   | 2 +-
 9 2 files changed, 2 insertions(+), 5 deletions(-)
10
11diff --git a/src/common.h b/src/common.h
12index 80a3d6e..3c77f48 100644
13--- a/src/common.h
14+++ b/src/common.h
15@@ -77,12 +77,9 @@ static inline int bitcount(unsigned v)
16 	return (((v + (v>>4)) & 0xF0F0F0F) * 0x1010101) >> 24;
17 }
18 
19-/* Return index of first bit [0-31], -1 on zero */
20-#define firstbit(v) (__builtin_ffs(v) - 1)
21-
22 /* boost-style foreach bit */
23 #define foreach_bit(i, m)						\
24-	for (i = firstbit(m); i >= 0; i = firstbit((m) & (~0U << (i + 1))))
25+	for (i = -1; (m) & ~0U << (i + 1);) if ((m) & 1U << ++i)
26 
27 /* robust system ioctl calls */
28 #define SYSCALL(call) while (((call) == -1) && (errno == EINTR))
29diff --git a/src/core.c b/src/core.c
30index 0d91c0b..20ce0c6 100644
31--- a/src/core.c
32+++ b/src/core.c
33@@ -304,7 +304,7 @@ static void apply_typeA_changes(struct mtdev_state *state,
34 			break;
35 		}
36 		if (id != MT_ID_NULL) {
37-			slot = firstbit(unused);
38+			foreach_bit(slot, unused) break;
39 			push_slot_changes(state, &data[i], prop[i], slot, syn);
40 			SETBIT(used, slot);
41 			CLEARBIT(unused, slot);
42-- 
432.25.0
44