Add fmt_decimal and count_digits routines

.gitignore

@@ -1,2 +1,3 @@
 *.o
 *.elf
+.gdb_history

Makefile

@@ -45,6 +45,12 @@ tests/math_mod.elf: hex.o math.o tests/math_mod.o
 tests/math_clz.elf: hex.o math.o tests/math_clz.o
 	$(LD) -m elf32lriscv -T link.ld $^ -o $@
 
+tests/fmt_count_digits.elf: hex.o math.o fmt.o tests/fmt_count_digits.o
+	$(LD) -m elf32lriscv -T link.ld $^ -o $@
+
+tests/fmt_decimal.elf: math.o fmt.o tests/fmt_decimal.o
+	$(LD) -m elf32lriscv -T link.ld $^ -o $@
+
 tests/btohex.elf: mem.o hex.o debug.o tests/btohex.o
 	$(LD) -m elf32lriscv -T link.ld $^ -o $@
 

fmt.s

@@ -0,0 +1,83 @@
+.global fmt_decimal
+.global count_digits
+
+.extern clz
+.extern divmod
+
+.section .rodata
+
+hexchars:
+  .ascii "0123456789ABCDEF"
+
+powers10:
+    .word 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000
+    .set powers10_end, .
+
+.text
+
+# Write decimal representation of word into buffer
+#    arguments:
+#       a0: value to format
+#       a1: address of buffer to write to
+#           buffer must have room for at least 10 bytes
+#   temporaries used:
+#       t0
+#    return:
+#       a0: length of string written to buffer
+fmt_decimal:
+    # until the value is zero:
+    #    divmod value by 10
+    #    write remainder to output buffer as ASCII char
+    #    increment string length
+    #    subtract remainder from value
+    # if we can know how many digits there will be up front we can write to the buffer
+    # in the right order, if not the buffer will have to be reversed at the end
+    addi sp, sp, -16
+    sw ra, 12(sp)
+    sw s1, 8(sp)
+    sw s0, 4(sp)
+    mv s0, a0         # save value in a0 to s0
+    mv s1, a1         # save buffer address to s1
+    jal count_digits
+    sw a0, 0(sp)      # save digit count to return at the end
+    addi a0, a0, -1   # a0 -= 1
+    add s1, s1, a0    # add the digit count to the buffer address
+1:
+    mv a0, s0         # load dividend from s0
+    li a1, 10         # set divisor to 10
+    jal divmod        # divmod value by 10, a1 = remainder
+    mv s0, a0         # move quotent to s0
+    addi a1, a1, 0x30 # turn remainder into ASCII digit
+    sb a1, 0(s1)      # write the digit to the output buffer
+    addi s1, s1, -1   # decrement buffer address
+    bnez s0, 1b
+
+    lw a0, 0(sp)      # load digit count into a0
+    lw s0, 4(sp)
+    lw s1, 8(sp)
+    lw ra, 12(sp)
+    addi sp, sp, 16
+    ret
+
+
+# Calculate number of decimal digits input word has.
+#    arguments:
+#       a0: value to count
+#    return:
+#       a0: count of decimal digits
+count_digits:
+    mv a2, a0           # a2 = value
+    la a1, powers10     # a1 = powers10
+    la a4, powers10_end # a4 = powers10_end
+    li a0, 0            # a0 = powers array offset * 4
+1:
+    bgeu a1, a4, 2f     # if a1 >= powers10_end return 10
+    lw a3, 0(a1)        # a3 = load value from powers array
+    addi a0, a0, 1      # increment offset
+    bltu a2, a3, 3f     # if a2 < a3 return
+    addi a1, a1, 4      # a1 = index into powers array
+    j 1b                # loop
+2:
+    li a0, 10
+3:
+    ret

tests/fmt_count_digits.s

@@ -0,0 +1,50 @@
+# Test for count_digits
+
+.org 0
+# Provide program starting address to linker
+.global _start
+
+.extern count_digits
+.extern tohex
+
+/* newlib system calls */
+.set SYSEXIT,  93
+.set SYSWRITE, 64
+
+.section .rodata
+
+inputs:
+    .word 0, 1, 2, 3, 9, 10, 100, 999, 1000, 0x8000000, 0x80000000 # TODO: negative values
+inputs_end:
+
+.section .bss
+
+buf: .skip 11
+
+.text
+
+_start:
+    li a0, '\n'
+    la a1, buf
+    sb a0, 8(a1)        # append newline to buf
+
+    la s0, inputs       # init loop variables
+    la s1, inputs_end
+loop:
+    lw a0, 0(s0)
+    jal count_digits
+    la a1, buf
+    jal tohex
+
+    li t0, SYSWRITE     # "write" syscall
+    li a0, 1            # 1 = standard output (stdout)
+    la a1, buf          # load address of output string
+    li a2, 9            # length of output string
+    ecall               # invoke syscall to print the string
+
+    addi s0, s0, 4      # increment input pointer to the next input
+    bltu s0, s1, loop   # if the input address is less than inputs_end, loop
+
+    li t0, SYSEXIT      # "exit" syscall
+    la a0, 0            # Use 0 return code
+    ecall               # invoke syscall to terminate the program

tests/fmt_decimal.s

@@ -0,0 +1,52 @@
+# Test for fmt_decimal
+
+.org 0
+# Provide program starting address to linker
+.global _start
+
+.extern fmt_decimal
+
+/* newlib system calls */
+.set SYSEXIT,  93
+.set SYSWRITE, 64
+
+.section .rodata
+
+inputs:
+    .word 0, 1, 2, 3, 9, 10, 100, 0x80000000
+inputs_end:
+
+.section .bss
+
+buf: .skip 11
+
+.text
+
+_start:
+    # li a0, '\n'
+    # la a1, buf
+    # sb a0, 8(a1)        # append newline to buf
+
+    la s0, inputs       # init loop variables
+    la s1, inputs_end
+loop:
+    lw a0, 0(s0)
+    la a1, buf
+    jal fmt_decimal
+    mv a2, a0           # store length of decimal string into a2 for use by SYS_write
+    li a0, '\n'
+    la a1, buf
+    add t0, a1, a2      # offset to end of buffer
+    sb a0, 0(t0)        # append newline to buf
+    li t0, SYSWRITE     # "write" syscall
+    li a0, 1            # 1 = standard output (stdout)
+    la a1, buf          # load address of output string
+    addi a2, a2, 1      # add one to length for newline
+    ecall               # invoke syscall to print the string
+
+    addi s0, s0, 4      # increment input pointer to next inputs
+    bltu s0, s1, loop   # if the input address is less than inputs_end, loop
+
+    li t0, SYSEXIT      # "exit" syscall
+    la a0, 0            # Use 0 return code
+    ecall               # invoke syscall to terminate the program

tests/test_fmt.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+test_count_digits() {
+  result=$("${QEMU}" -B 0x80000000 -s 2k tests/fmt_count_digits.elf)
+  expected=$(cat << END
+00000001
+00000001
+00000001
+00000001
+00000001
+00000002
+00000003
+00000003
+00000004
+00000009
+0000000A
+END
+)
+
+  test $? -eq 0 && test "$result" = "$expected"
+}
+
+test_fmt_decimal() {
+  result=$("${QEMU}" -B 0x80000000 -s 2k tests/fmt_decimal.elf)
+  expected=$(cat << END
+0
+1
+2
+3
+9
+10
+100
+2147483648
+END
+)
+
+  test $? -eq 0 && test "$result" = "$expected"
+}