arm: Add string-fza.h

While arm has the more important string functions in assembly,
there are still a few generic routines used.

Use the UQSUB8 insn for testing of zeros.

Checked on armv7-linux-gnueabihf

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/sysdeps/arm/armv6t2/string-fza.h b/sysdeps/arm/armv6t2/string-fza.h
new file mode 100644 (file)
index 0000000..76274cc
--- /dev/null
+++ b/sysdeps/arm/armv6t2/string-fza.h
@@ -0,0 +1,67 @@
+/* Zero byte detection; basics.  ARM version.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _STRING_FZA_H
+#define _STRING_FZA_H 1
+
+#include <string-misc.h>
+#include <string-optype.h>
+
+/* The functions return a byte mask.  */
+typedef op_t find_t;
+
+/* This function returns at least one bit set within every byte
+   of X that is zero.  */
+static __always_inline find_t
+find_zero_all (op_t x)
+{
+  /* Use unsigned saturated subtraction from 1 in each byte.
+     That leaves 1 for every byte that was zero.  */
+  op_t ones = repeat_bytes (0x01);
+  return __builtin_arm_uqsub8 (ones, x);
+}
+
+/* Identify bytes that are equal between X1 and X2.  */
+static __always_inline find_t
+find_eq_all (op_t x1, op_t x2)
+{
+  return find_zero_all (x1 ^ x2);
+}
+
+/* Identify zero bytes in X1 or equality between X1 and X2.  */
+static __always_inline find_t
+find_zero_eq_all (op_t x1, op_t x2)
+{
+  return find_zero_all (x1) | find_zero_all (x1 ^ x2);
+}
+
+/* Identify zero bytes in X1 or inequality between X1 and X2.  */
+static __always_inline find_t
+find_zero_ne_all (op_t x1, op_t x2)
+{
+  /* Make use of the fact that we'll already have ONES in a register.  */
+  op_t ones = repeat_bytes (0x01);
+  return find_zero_all (x1) | (find_zero_all (x1 ^ x2) ^ ones);
+}
+
+/* Define the "inexact" versions in terms of the exact versions.  */
+#define find_zero_low          find_zero_all
+#define find_eq_low            find_eq_all
+#define find_zero_eq_low       find_zero_eq_all
+
+#endif /* _STRING_FZA_H */