[PATCH v3 12/15] riscv: add vectorized strspn

[Pincheng Wang]

The vector implementation builds a 256-byte accept table on the stack and
scans the string in vector-length chunks using fault-only-first loads
(vle8ff.v) with an indexed gather into the table, so the scan never
crosses into an unmapped page and the gather only touches the fully-mapped
table.  This provides significant performance improvements on RVV-capable
hardware.  Use conditional compilation to fall back to the generic
implementation when __riscv_vector is not available, maintaining
compatibility with non-vector RISC-V systems.

Signed-off-by: Pincheng Wang <pincheng.plct@isrc.iscas.ac.cn>
---
 newlib/libc/machine/riscv/Makefile.inc |  4 ++-
 newlib/libc/machine/riscv/strspn-asm.S | 47 ++++++++++++++++++++++++++
 newlib/libc/machine/riscv/strspn.c     |  5 +++
 3 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 newlib/libc/machine/riscv/strspn-asm.S
 create mode 100644 newlib/libc/machine/riscv/strspn.c

diff --git a/newlib/libc/machine/riscv/Makefile.inc b/newlib/libc/machine/riscv/Makefile.inc
index fae228e43..55f137a3c 100644
--- a/newlib/libc/machine/riscv/Makefile.inc
+++ b/newlib/libc/machine/riscv/Makefile.inc
@@ -41,4 +41,6 @@ libc_a_SOURCES += \
 	%D%/strnlen-asm.S \
 	%D%/strnlen.c \
 	%D%/strrchr-asm.S \
-	%D%/strrchr.c
+	%D%/strrchr.c \
+	%D%/strspn-asm.S \
+	%D%/strspn.c
diff --git a/newlib/libc/machine/riscv/strspn-asm.S b/newlib/libc/machine/riscv/strspn-asm.S
new file mode 100644
index 000000000..03f3a6b25
--- /dev/null
+++ b/newlib/libc/machine/riscv/strspn-asm.S
@@ -0,0 +1,47 @@
+#include <sys/asm.h>
+
+#if defined(__riscv_vector) && !defined(__riscv_e) && !defined(__OPTIMIZE_SIZE__) && !defined(PREFER_SIZE_OVER_SPEED)
+/* size_t strspn(const char *a0, const char *a1)
+   Length of the initial segment of a0 made up entirely of bytes in a1.
+   Build a 256-byte "accept" table from a1 (NUL is never marked, since a1 is
+   a string), then scan a0 and stop at the first byte not in the set; a NUL
+   in a0 stops the scan naturally.  The scan uses vle8ff (page-boundary safe);
+   the gather only touches the fully-mapped 256-byte table.  */
+ENTRY(strspn)
+  addi sp, sp, -256
+  li t1, 256
+  mv t0, sp
+.Lzero:
+  vsetvli t2, t1, e8, m8, ta, ma
+  vmv.v.i v8, 0
+  vse8.v v8, (t0)
+  add t0, t0, t2
+  sub t1, t1, t2
+  bnez t1, .Lzero
+  li t1, 1
+.Lbuild:
+  lbu t0, 0(a1)
+  beqz t0, .Lscan
+  add t2, sp, t0
+  sb t1, 0(t2)
+  addi a1, a1, 1
+  j .Lbuild
+.Lscan:
+  mv a2, a0
+.Lloop:
+  vsetvli t3, zero, e8, m1, ta, ma
+  vle8ff.v v8, (a0)
+  csrr t3, vl
+  vluxei8.v v16, (sp), v8       /* gather accept[a0[i]] */
+  vmseq.vi v0, v16, 0           /* lanes NOT in the accept set */
+  vfirst.m t4, v0
+  bgez t4, .Lfound
+  add a0, a0, t3
+  j .Lloop
+.Lfound:
+  add a0, a0, t4
+  sub a0, a0, a2
+  addi sp, sp, 256
+  ret
+END(strspn)
+#endif
diff --git a/newlib/libc/machine/riscv/strspn.c b/newlib/libc/machine/riscv/strspn.c
new file mode 100644
index 000000000..8d9d3fba9
--- /dev/null
+++ b/newlib/libc/machine/riscv/strspn.c
@@ -0,0 +1,5 @@
+#if defined(__OPTIMIZE_SIZE__) || defined(PREFER_SIZE_OVER_SPEED) || !defined(__riscv_vector) || defined(__riscv_e)
+# include "../../string/strspn.c"
+#else
+/* strspn defined in strspn-asm.S */
+#endif
-- 
2.39.5