From: Heiko Carstens <hca@linux.ibm.com>
Date: Fri, 6 Oct 2023 13:42:41 +0000 (+0200)
Subject: s390: provide word-at-a-time implementation
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=76292d7243f809486ec26dd6cd3436dbcb9e5319;p=linux.git

s390: provide word-at-a-time implementation

Provide an s390 specific word-at-a-time implementation. Compared to the
generic variant the generated code for has_zero() is slightly
better. However find_zero() is much simpler since it reuses the result
of __fls() aka flogr() and now comes without any conditional branches,
while the generic variant has three of them.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
---

diff --git a/arch/s390/include/asm/word-at-a-time.h b/arch/s390/include/asm/word-at-a-time.h
new file mode 100644
index 0000000000000..09b37541a175b
--- /dev/null
+++ b/arch/s390/include/asm/word-at-a-time.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_WORD_AT_A_TIME_H
+#define _ASM_WORD_AT_A_TIME_H
+
+#include <linux/kernel.h>
+#include <asm/bitsperlong.h>
+
+struct word_at_a_time {
+	const unsigned long bits;
+};
+
+#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x7f) }
+
+static inline unsigned long prep_zero_mask(unsigned long val, unsigned long data, const struct word_at_a_time *c)
+{
+	return data;
+}
+
+static inline unsigned long create_zero_mask(unsigned long data)
+{
+	return __fls(data);
+}
+
+static inline unsigned long find_zero(unsigned long data)
+{
+	return (data ^ (BITS_PER_LONG - 1)) >> 3;
+}
+
+static inline unsigned long has_zero(unsigned long val, unsigned long *data, const struct word_at_a_time *c)
+{
+	unsigned long mask = (val & c->bits) + c->bits;
+
+	*data = ~(mask | val | c->bits);
+	return *data;
+}
+
+static inline unsigned long zero_bytemask(unsigned long data)
+{
+	return ~1UL << data;
+}
+
+#endif /* _ASM_WORD_AT_A_TIME_H */