x86/string: add some optimized string functions

2 files changed, 95 insertions, 0 deletions

diff --git a/arch/x86/machine/param.h b/arch/x86/machine/param.h
index 80c8de9..ce373c8 100644
--- a/arch/x86/machine/param.h
+++ b/arch/x86/machine/param.h
@@ -50,6 +50,14 @@
 #define __read_mostly __section(".data.read_mostly")
 
 /*
+ * Provide architecture-specific string functions.
+ */
+#define ARCH_STRING_MEMCPY
+#define ARCH_STRING_MEMMOVE
+#define ARCH_STRING_MEMSET
+#define ARCH_STRING_MEMCMP
+
+/*
  * System timer frequency.
  *
  * The selected value of 200 translates to a period of 5ms, small enough to
diff --git a/arch/x86/machine/string.c b/arch/x86/machine/string.c
new file mode 100644
index 0000000..2ea8392
--- /dev/null
+++ b/arch/x86/machine/string.c
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2014 Richard Braun.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <kern/param.h>
+#include <kern/stddef.h>
+#include <kern/string.h>
+
+#ifdef ARCH_STRING_MEMCPY
+void *
+memcpy(void *dest, const void *src, size_t n)
+{
+    void *orig_dest;
+
+    orig_dest = dest;
+    asm volatile("cld; rep movsb" : "+D" (dest), "+S" (src), "+c" (n));
+    return orig_dest;
+}
+#endif /* ARCH_STRING_MEMCPY */
+
+#ifdef ARCH_STRING_MEMMOVE
+void *
+memmove(void *dest, const void *src, size_t n)
+{
+    void *orig_dest;
+
+    orig_dest = dest;
+
+    if (dest <= src)
+        asm volatile("cld; rep movsb" : "+D" (dest), "+S" (src), "+c" (n));
+    else {
+        dest += n - 1;
+        src += n - 1;
+        asm volatile("std; rep movsb" : "+D" (dest), "+S" (src), "+c" (n));
+    }
+
+    return orig_dest;
+}
+#endif /* ARCH_STRING_MEMMOVE */
+
+#ifdef ARCH_STRING_MEMSET
+void *
+memset(void *s, int c, size_t n)
+{
+    void *orig_s;
+
+    orig_s = s;
+    asm volatile("cld; rep stosb" : "+D" (s), "+c" (n) : "a" (c));
+    return orig_s;
+}
+#endif /* ARCH_STRING_MEMSET */
+
+#ifdef ARCH_STRING_MEMCMP
+int
+memcmp(const void *s1, const void *s2, size_t n)
+{
+    unsigned char zf, c1, c2;
+
+    if (n == 0)
+        return 0;
+
+    asm volatile("cld\n"
+                 "repe cmpsb\n"
+                 "sete %0\n"
+                 : "=g" (zf), "+D" (s1), "+S" (s2), "+c" (n));
+
+    if (zf)
+        return 0;
+
+    c1 = *(((const unsigned char *)s1) - 1);
+    c2 = *(((const unsigned char *)s2) - 1);
+    return (int)c1 - (int)c2;
+}
+#endif /* ARCH_STRING_MEMCMP */