kvisc/ka/crt/fmt/doprnt.k

; The OS/K Team licenses this file to you under the MIT license.
; See the LICENSE file in the project root for more information.

;
; typedef int (*PUTC)(int ch)
; int doprnt(PUTC putc, int n, const char *fmt, va_list ap)
;
doprnt:
    push rbp
    mov rbp, rsp

    push r12
    push r13
    push r14
    push r15
    push r16
    push r17

    mov r12, ax2        ; fmt
    mov r14, ax3        ; va_list
    mov r15, ax1        ; n
    mov r16, zero       ; return value
    mov r17, ax0        ; putc

.main_loop:
    ; find '%' or null-terminator
    mov rcx, STRLEN_MAX
    mov r13, r12
    scasb.rep.nz r13, '%'

    ; everything below r13 is a regular character; print it
.print_regular:
    b.z r12, r13, .check_modf

    call .doput, b[r12]

    inc r12, 1
    jmp .print_regular

.check_modf:
    ; did we find a '%' ?
    ; if not, then we found fmt's null-terminator; we're done
    b.nz b[r12], '%', .epilogue

    ; we did find a modifier / '%'
    mov rax, b[r12+1]
    inc r12, 2

    b.z rax, 's', .modf_s
    b.z rax, 'c', .modf_c
    b.z rax, 'p', .modf_p
    b.z rax, 'x', .modf_x
    b.z rax, 'd', .modf_d
    b.z rax, 'o', .modf_o
    b.z rax, 'b', .modf_b
    b.z rax, '%', .modf_percent

    ; unrecognized
    jmp .bad_modifier

.modf_s:
    ; get string address
    mov r13, q[r14]
    inc r14, 8

    b.z r13, zero, .nullstring

.print_string:
    mov ax0, b[r13]
    b.z ax0, zero, .main_loop

    inc r13, 1
    call .doput

    jmp .print_string

.modf_c:
    call .doput, q[r14]
    inc r14, 8

    jmp .main_loop

.modf_p:
    call .doput, '0'
    call .doput, 'x'
    ; Fallthrough

.modf_x:
    mov ax2, 16
    jmp .print_number

.modf_d:
    mov ax2, 10
    jmp .print_number

.modf_o:
    mov ax2, 8
    jmp .print_number

.modf_b:
    mov ax2, 2
    jmp .print_number

.print_number:
    ; allocate itoa conversion buffer
    dec rsp, 80
    mov r13, rsp

    ; assume modifier already set up ax2
    call itoa, rsp, q[r14]
    inc r14, 8

.print_itoa_buf:
    mov ax0, b[r13]

    cmp ax0, zero
    inc.z rsp, 80
    jmp.z .main_loop

    inc r13, 1
    call .doput
    jmp .print_itoa_buf

.modf_percent:
    call .doput, '%'
    jmp .main_loop

.bad_modifier:
    ; print "%?" to clearly indicate that something is wrong
    call .doput, '%'
    call .doput, '?'

    jmp .main_loop

.nullstring:
    ; %s was passed a NULL
    call .doput, '('
    call .doput, 'n'
    call .doput, 'u'
    call .doput, 'l'
    call .doput, 'l'
    call .doput, ')'

    jmp .main_loop

.epilogue:
    mov rax, r16
    
    pop r17
    pop r16
    pop r15
    pop r14
    pop r13
    pop r12

    leave
    ret
;
; prints ax0
;
.doput:
    ; update print count
    inc r16, 1

    ; if n==0, don't print
    ; we follow the C convention that sprintf()-like functions
    ; should return the number of characters that would have
    ; been printed/written if 'n' were big enough
    cmp r15, zero
    ret.z

    ; if n>0, decrement n and print
    dec r15, 1
    call r17
    
    ; did putc fail?
    mov.axnz r15, zero     ; yes, so artificially set n=0

    ret