Remove old test code

There is some code that I had there after messing with some of the
topics on Uros' blog (https://popovicu.com/), but that became irrelevant
after working on some other projects (e.g. fbos) or on other examples.

This commit also brings about a major overhaul on the structure of the
project. Hopefully it's now at a more ready state.

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

1 files changed, 111 insertions, 0 deletions

diff --git a/arch/riscv/user/basics/string.S b/arch/riscv/user/basics/string.S
new file mode 100644
index 0000000..3878074
--- /dev/null
+++ b/arch/riscv/user/basics/string.S
@@ -0,0 +1,111 @@
+.text
+
+.globl reverse_string
+.type reverse_string, @function
+
+// char * reverse_string(char *str);
+reverse_string:
+    // Return early on null pointer.
+    beq a0, zero, end
+
+    // Preserve the original pointer.
+    addi sp, sp, -8
+    sd a0, 0(sp)
+
+    // Set `t0` to point to the end of the string.
+    add t0, a0, zero
+set_end_ptr:
+    lbu t2, 0(t0)
+    beq t2, zero, end_ptr_done
+    addi t0, t0, 1
+    j set_end_ptr
+
+    // We are done iterating, if `a0` and `t0` are equal, then there's nothing
+    // to be done and we can return early. Otherwise decrement `t0` so it points
+    // to the byte right before the null termination.
+end_ptr_done:
+    beq a0, t0, reverse_done
+    addi t0, t0, -1
+
+reverse_loop:
+    // Swap values between the two pointers.
+    lb t1, 0(a0)
+    lb t2, 0(t0)
+    sb t1, 0(t0)
+    sb t2, 0(a0)
+
+    // Move pointers and check whether the pointers have already crossed. If
+    // they have not crossed yet there is still looping to be done. Otherwise
+    // we are done.
+    addi a0, a0, 1
+    addi t0, t0, -1
+    bltu a0, t0, reverse_loop
+
+reverse_done:
+    // Restore things back and return to the caller.
+    ld a0, 0(sp)
+    addi sp, sp, 8
+end:
+    jr ra
+
+.globl is_palindrome
+.type is_palindrome, @function
+
+// bool is_palindrome(char *str);
+is_palindrome:
+    // Return early on null pointer.
+    beq a0, zero, palindrome_no
+
+    // Set `t0` to point to the end of the string.
+    add t0, a0, zero
+pal_set_end_ptr:
+    lbu t2, 0(t0)
+    beq t2, zero, pal_end_ptr_done
+    addi t0, t0, 1
+    j pal_set_end_ptr
+
+    // We are done iterating, if `a0` and `t0` are equal, then there's nothing
+    // to be done and we can return early. Otherwise decrement `t0` so it points
+    // to the byte right before the null termination.
+pal_end_ptr_done:
+    beq a0, t0, palindrome_no
+    addi t0, t0, -1
+
+pal_loop:
+    // Swap values between the two pointers.
+    lb t1, 0(a0)
+    lb t2, 0(t0)
+    bne t1, t2, palindrome_no
+
+    // Move pointers and check whether the pointers have already crossed. If
+    // they have not crossed yet there is still looping to be done. Otherwise
+    // we are done.
+    addi a0, a0, 1
+    addi t0, t0, -1
+    bleu a0, t0, pal_loop
+
+palindrome_yes:
+    li a0, 1
+    jr ra
+
+palindrome_no:
+    li a0, 0
+    jr ra
+
+.globl mstrcmp
+.type mstrcmp, @function
+
+// int mstrcmp(const char *, const char *);
+mstrcmp:
+1:
+	lbu t0, 0(a0)
+	lbu t1, 0(a1)
+	bne t0, t1, 2f
+	addi a0, a0, 1
+	addi a1, a1, 1
+	bnez t0, 1b
+	li a0, 0
+	ret
+2:
+	sub a0, t0, t1
+	ret