string: use gint's optimized memset (DONE)

CMakeLists.txt

@@ -172,6 +172,7 @@ if(sh-generic IN_LIST TARGET_FOLDERS)
     src/libc/setjmp/target/sh-generic/setjmp.S
     src/libc/setjmp/target/sh-generic/longjmp.S
     src/libc/string/target/sh-generic/memchr.S
+    src/libc/string/target/sh-generic/memset.S
     src/libc/string/target/sh-generic/strlen.S
     src/target/sh-generic/cpucap.c)
 endif()

src/libc/string/memset.c

@@ -1,16 +1,13 @@
 #include <string.h>
 #include <stdint.h>
 
-/*
-** The  memset()  function fills the first n bytes of the memory area pointed to
-** by s with the constant byte c.
-**
-** TODO: use DMA !
-** TODO: use DSP ?
-*/
+#ifndef __SUPPORT_ARCH_SH
+
 void *memset(void *s, int c, size_t n)
 {
 	while ((int)--n >= 0)
 		((uint8_t *) s)[n] = c;
 	return (s);
 }
+
+#endif /*__SUPPORT_ARCH_SH*/

src/libc/string/target/sh-generic/memset.S

@@ -0,0 +1,70 @@
+.global _memset
+.text
+
+_memset:
+	tst	r6, r6
+	bt	.zero
+
+	/* We'll fill from the end */
+	mov	r4, r3
+	add	r6, r4
+
+	/* When setting less than 64 bytes, use the naive method */
+	mov	#64, r0
+	cmp/ge	r6, r0
+	bt	_naive_memset
+
+	mov	#3, r2
+
+	/* Make a 4-byte filler */
+	mov	r5, r0
+	shll8	r5
+	or	r5, r0
+	mov	r0, r5
+	shll16	r5
+	or	r5, r0
+
+_memset_align:
+	/* 4-align the destination */
+	mov.b	r0, @-r4
+	tst	r2, r4
+	bf/s	_memset_align
+	dt	r6
+
+	mov	#40, r2
+
+.aligned4_32:
+	add	#-32, r4
+	add	#-32, r6
+	mov.l	r0, @(28,r4)
+	mov.l	r0, @(24,r4)
+	mov.l	r0, @(20,r4)
+	mov.l	r0, @(16,r4)
+	mov.l	r0, @(12,r4)
+	mov.l	r0, @(8,r4)
+	mov.l	r0, @(4,r4)
+	cmp/ge	r6, r2
+	bf/s	.aligned4_32
+	mov.l	r0, @r4
+
+	mov	#8, r2
+
+.aligned4_4:
+	mov.l	r0, @-r4
+	cmp/ge	r6, r2
+	bf/s	.aligned4_4
+	add	#-4, r6
+
+_naive_memset:
+	/* Tight loop copy one byte */
+	dt	r6
+	bf/s	_naive_memset
+	mov.b	r5, @-r4
+
+.end:
+	rts
+	mov	r3, r0
+
+.zero:
+	rts
+	mov	r4, r0