1 files changed, 67 insertions, 0 deletions
diff --git a/boot/common-boot.s b/boot/common-boot.s
index 0cf31f1..26dad8d 100644
--- a/boot/common-boot.s
+++ b/boot/common-boot.s
@@ -2,6 +2,7 @@
 .global _write_out, _read_file, _write_error, _put_char, _printi
 .global _get, _memcmp, _memchr, _memmem, _memcpy
 .global _divide_by_zero_error, _exit
+.global _strings_index
 
 .section .rodata
 
@@ -424,3 +425,69 @@ _memcpy:
 .Lmemcpy_end:
 	mv a0, t0
 	ret
+
+# Searches for a string in a string array.
+#
+# Parameters:
+# a0 - Number of elements in the string array.
+# a1 - String array.
+# a2 - Needle length.
+# a3 - Needle.
+#
+# Sets a0 to the 1-based index of the needle in the haystack or to 0 if the
+# element could not be found.
+.type _strings_index, @function
+_strings_index:
+	# Prologue.
+	addi sp, sp, -32
+	sw ra, 28(sp)
+	sw s0, 24(sp)
+	addi s0, sp, 32
+
+	sw s1, 20(sp)
+	mv s1, a0
+	sw s2, 16(sp)
+	mv s2, a1
+	sw s3, 12(sp)
+	mv s3, a2
+	sw s4, 8(sp)
+	mv s4, a3
+	sw s5, 4(sp)
+	li s5, 0 # Index counter.
+
+.Lstrings_index_loop:
+	addi s5, s5, 1
+	beqz s1, .Lstrings_index_missing
+
+	lw a2, (s2) # Read the length of the current element in the haystack.
+	bne a2, s3, .Lstrings_index_next # Lengths don't match, skip the iteration.
+
+	addi a0, s2, 4
+	mv a1, s4
+	call _memcmp
+
+	beqz a0, .Lstrings_index_end
+
+.Lstrings_index_next:
+	addi s2, s2, 4
+	add s2, s2, a2
+	addi s1, s1, -1
+	j .Lstrings_index_loop
+
+.Lstrings_index_missing:
+	li s5, 0
+
+.Lstrings_index_end:
+	mv a0, s5
+
+	lw s1, 20(sp)
+	lw s2, 16(sp)
+	lw s3, 12(sp)
+	lw s4, 8(sp)
+	lw s5, 4(sp)
+
+	# Epilogue.
+	lw ra, 28(sp)
+	lw s0, 24(sp)
+	add sp, sp, 32
+	ret