Int to string conversion

Initially only binary output

src/int_to_string.asm

@@ -0,0 +1,66 @@
+include errno
+
+; Convert integer to string
+; Arguments:
+; r1 - Integer
+; r2 - Start of buffer
+; r3 - Buffer length
+; r4 - Base (2, 8, 10, or 16)
+; Result:
+; none
+; Clobbers:
+; Based on specialization
+pub auto:
+cmp r4, 2
+je bin
+mov flags, errno.INTTOSTR_BAD_BASE
+jmp r13
+
+; Convert integer to binary string
+; Arguments:
+; r1 - Integer
+; r2 - Start of buffer (assumed 'big enough')
+; r3 - Buffer length (ignored)
+; Result:
+; none
+; Clobbers:
+; flags
+; r4 - counter
+; r5 - result character
+pub bin:
+mov r4, 31
+cmp r2, 2
+jl badbuffer
+
+bin_find_one:
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 1
+sub r4, r4, 1
+
+cmp r4, 0               ; Start printing if last bit ...
+jl bin_print
+cmp r5, zr              ; .. or if nonzero
+je bin_find_one
+
+add flags, r4, 3        ; Check buffer size
+cmp flags, r3
+ja badbuffer
+
+bin_print:
+add r5, r5, 0x30 ; '0'  ; Add digit to buffer
+store_8 [r2], r5
+add r2, r2, 1
+cmp r4, 0               ; Done if last bit
+jl done
+lsr r5, r1, r4          ; Select bit and advance counter
+and r5, r5, 1
+sub r4, r4, 1
+jmp bin_print
+
+badbuffer:
+mov flags, errno.INTTOSTR_BAD_BUFFER
+jmp r13
+
+done:
+store_8 [r2], zr
+jmp r13