## LSU EE 4720 -- Fall 2019 -- Computer Architecture # ## Histogram Example Program # Time-stamp: <22 January 2019, 15:24:06 CST, koppel@cyc.ece.lsu.edu> ## Contents # # histo. (Computes the histogram) # Data Section # Test routine. (Calls histogram program and prints table.) # upper. (Converts string to upper case.) # strlen. (Computes the length of a string.) ################################################################################ ## histo: Compute Character Usage Histogram .text histo: ## Register Usage # # Call: $a0 String to analyze. # $a1 Address of 26-element histogram table. # Each element is a 4-byte integer. # Initially all elements zero. # Return: # Let h = $a1. # h[0]: Number of A's. # h[1]: Number of B's. # ... addi $s1, $ra, 0 # Make a copy of the return address. jal upper # Convert to upper case. addi $s0, $a0, 0 # Make a copy of string start address. addi $a0, $s0, 0 # Restore string start address. LOOP: lb $t0, 0($a0) # Load next character. beq $t0, $0, DONE # Jump out of loop if at end of string. addi $a0, $a0, 1 # Increment to address of next character. addi $t0, $t0, -65 # Set $t0 to table index. ( A -> 0, B -> 1, etc.) sltiu $t3, $t0, 26 # If $t0 is >= 26 then it's not a letter .. beq $t3, $0, LOOP # .. and so get the next char. (Note unsigned cmp.) sll $t0, $t0, 2 # Scale index based on table element size (4). add $t2, $a1, $t0 # Compute address of table element. lw $t1, 0($t2) # Load table element. Value is # of times char seen. addi $t1, $t1, 1 # We're seeing the char again, so add one .. j LOOP sw $t1, 0($t2) # .. and store the result back in the table. DONE: jr $s1 # Return using the saved return address. nop ################################################################################ ## Test Routine # # Calls histogram program (histo) then prints table. # ## Input string for testing histo. # .data doi: .ascii "[]\^_`@?>={|}~\n" # Test some out-of-range characters. .ascii "\n" .ascii "Do you know what it means to miss New Orleans" .ascii "And miss it each night and day" .ascii "I know I'm not wrong... this feeling's gettin' stronger" .ascii "The longer, I stay away" .ascii "Miss them moss covered vines...the tall sugar pines" .ascii "Where mockin' birds used to sing" .ascii "And I'd like to see that lazy Mississippi...hurryin' into spring" .ascii "" .ascii "The moonlight on the bayou.......a creole tune.... that fills the air" .ascii "I dream... about magnolias in bloom......and I'm wishin I was there" .ascii "" .ascii "Do you know what it means to miss new orleans" .ascii "When that's where you left your heart" .ascii "And there's one thing more...i miss the one I care for" .ascii "More than I miss New Orleans" .ascii "" .asciiz "-- Louis Armstrong" msg: .asciiz "Letter %/t3/c count: %/t1/3d (%/f4/6.2f%%) %/t5/s\n"; .align 4 histogram_data: .space 104 stars: .space 40 TB_100: .double 100.0 # The constant 100, used to show percents. .text .globl __start __start: la $a0, doi la $a1, histogram_data addi $t1, $a1, 0 addi $t2, $t1, 100 L3: sw $0, 0($t1) bne $t1, $t2, L3 addi $t1, $t1, 4 la $t1, stars addi $t2, $t1, 40 addi $t3, $0, 42 # '*' L4: sb $t3, 0($t1) bne $t1, $t2, L4 addi $t1, $t1, 1 sb $0, 0($t1) jal strlen nop mtc1 $v0, $f2 cvt.d.w $f2, $f2 la $t3, TB_100 ldc1 $f4, 0($t3) div.d $f2, $f4, $f2 jal histo nop add $t0, $0, $0 addi $t3, $0, 64 addi $t4, $t3, 26 la $s1, histogram_data addi $v0, $0, 11 la $s2, stars addi $s2, $s2, 41 L2: lw $t1, 0($s1) addi $s1, $s1, 4 beq $t1, $0, TEST addi $t3, $t3, 1 srl $t6, $t1, 1 sub $t5, $s2, $t6 mtc1 $t1, $f0 cvt.d.w $f0, $f0 mul.d $f4, $f0, $f2 syscall TEST: bne $t3, $t4, L2 nop addi $v0, $0, 10 syscall ################################################################################ ## upper: Convert to Upper Case upper: ## Register Usage # # $a0: (Call) Address of string to convert. # # $a0: Address of character being examined. # $t1: Character being examined. # $t2: Comparison result. # # Example: Before: "aB." # After: "AB." ULOOP: lbu $t1, 0($a0) # Load character from string. addi $a0, $a0, 1 beq $t1, $0, UDONE slti $t2, $t1, 97 # < 'a' bne $t2, $0 ULOOP slti $t2, $t1, 123 # 'z' + 1 beq $t2, $0, ULOOP addi $t1, $t1, -32 j ULOOP sb $t1,-1($a0) UDONE: jr $ra nop ################################################################################ ## strlen: String Length strlen: ## Register Usage # # $a0: Address of first character of string. # $v0: Return value, the length of the string. # # $t0: Character being examined. # $t1: Address of current character being examined. # addi $t1, $a0, 0 SLOOP: lbu $t0, 0($t1) bne $t0, $0, SLOOP addi $t1, $t1, 1 addi $t1, $t1, -1 jr $ra sub $v0, $t1, $a0