Lab 06, Exercise 1, complete

Labs/Lab06/xfind.s

+# CSCI 206 Computer Organization & Programming
+
+# Date: 2011-09-19
+
+# Revised: 2019-11-04 for RISC-V
+
+#
+
+# Copyright (c) 2011 Bucknell University
+
+#
+
+# Permission is hereby granted, free of charge, to any individual or
+
+# institution obtaining a copy of this software and associated
+
+# documentation files (the "Software"), to use, copy, modify, and
+
+# distribute without restriction, provided that this copyright and
+
+# permission notice is maintained, intact, in all copies and
+
+# supporting
+
+# documentation.
+
+#
+
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
+
+# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
+
+# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+
+# NONINFRINGEMENT. IN NO EVENT SHALL BUCKNELL UNIVERSITY BE LIABLE FOR ANY
+
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH
+
+# THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+#
+
+#
+
+# Student name: Kyle Chrysler
+
+#
+
+#
+
+# This program uses a procedure xfind to find a particular character.
+
+# See detailed instructions in lab handout
+
+
+
+.data
+
+# Define constants here
+
+strprompt: .asciz "Enter a string to search:"
+
+charprompt: .asciz "Enter the character to search for:"
+
+
+
+# allocate 100 bytes to store the string
+
+string: .space 100
+
+
+
+.text
+
+
+
+main:
+
+	la a0, strprompt
+
+	li a7, 4			# print prompt string
+
+	ecall
+
+
+
+	la	a0, string		# load address of string
+
+	li a1, 100			# max input length
+
+	li a7, 8 			# read string
+
+	ecall
+
+
+
+	la a0, charprompt
+
+	li a7, 4			# print string
+
+	ecall
+
+
+
+	li a7, 12 			# read char
+
+	ecall
+
+
+
+	mv a1, a0			# move search char to a1
+
+	la a0, string			# load addr of string into a0
+	
+
+	jal	xfind			# call xfind
+
+
+
+# TODO
+
+# write code here to print the result of the
+
+# call to xfind
+	
+	li      a7, 34
+	
+	ecall
+	
+	li	a7, 10			# exit to OS
+
+	ecall
+
+
+
+# write the code of function xfind after this label
+
+xfind:
+	# TODO search the string pointed to by a0 for the character in a1
+
+	# if found, return the address of the first match
+
+	# if not found, return 0 (NULL)
+	lb t2, 0(a0)
+	beq t2, a1, exit
+	beq t2, zero, exitNull
+	addi a0, a0, 1
+	j xfind
+
+exitNull:
+	li a0, 0
+exit:
+	jr ra
+