Move string.S to the lib directory

It was weird enough to have it in the 'kernel' directory, as it's way
more fitting to have it on 'lib'.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 97 insertions, 0 deletions

diff --git a/lib/string.S b/lib/string.S
new file mode 100644
index 0000000..271e8f3
--- /dev/null
+++ b/lib/string.S
@@ -0,0 +1,97 @@
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     size_t strlen(const char *str)
+ *
+ * Returns (a0): string length.
+ * Parameter (a0): string to measure.
+ * Clobbers: t0, t1.
+ */
+.globl strlen
+.type strlen, @function
+strlen:
+	mv t1, a0
+1:
+	lbu t0, 0(t1)
+	beqz t0, 2f
+	addi t1, t1, 1
+	j 1b
+2:
+	sub a0, t1, a0
+	ret
+
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     int strcmp(const char *s1, const char *s2)
+ *
+ * Returns (a0): comparison result as in stdlib.
+ * Parameter (a0, a1): strings to compare.
+ * Clobbers: t0, t1.
+ */
+.globl strcmp
+.type strcmp, @function
+strcmp:
+1:
+	lbu t0, 0(a0)
+	lbu t1, 0(a1)
+	addi a0, a0, 1
+	addi a1, a1, 1
+	bne t0, t1, 2f
+	bnez t0, 1b
+	li a0, 0
+	ret
+2:
+	sub a0, t0, t1
+	ret
+
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     int memcmp(const void *ptr1, const void *ptr2, size_t n)
+ *
+ * Returns (a0): comparison result as in stdlib.
+ * Parameters (a0, a1): strings to compare.
+ * Clobbers: t0, t1.
+ */
+.global memcmp
+.type memcmp, @function
+memcmp:
+1:
+	lbu t0, 0(a0)
+	lbu t1, 0(a1)
+	bne t0, t1, 2f
+	addi a0, a0, 1
+	addi a1, a1, 1
+	addi a2, a2, -1
+	bnez a2, 1b
+	li a0, 0
+	ret
+2:
+	sub a0, t0, t1
+	ret
+
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     void memcpy(const void *dest, const void *src, size_t count)
+ *
+ * Parameter a0: destination string.
+ * Parameter a1: source string.
+ * Parameter a2: number of bytes to copy.
+ * Clobbers: t0.
+ */
+.global memcpy
+.type memcpy, @function
+memcpy:
+1:
+	beqz a2, 3f
+2:
+	lbu t0, 0(a1)
+	sb t0, 0(a0)
+	addi a0, a0, 1
+	addi a1, a1, 1
+	addi a2, a2, -1
+	bnez a2, 2b
+3:
+	ret