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:
    dump 0
    enter 8

    mov q[rbp-8], rbx
    mov q[rbp-16], nx0
    mov q[rbp-24], nx1
    mov q[rbp-32], nx2
    mov q[rbp-40], rdi
    mov q[rbp-48], rsi
    mov q[rbp-56], nx3

    mov rbx, ax2        ; fmt
    mov nx3, ax0        ; putc
    mov nx0, ax1        ; n
    xor nx1, nx1        ; return value
    xor nx2, nx2        ; index in va_list
    mov rsi, ax3        ; ap

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

.print_regular:
    ; everything below rdi is a regular character; print it
    b.e rbx, rdi, .check_modf

    mov ax0, b[rbx]
    call .doput

    inc rbx
    jmp .print_regular

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

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

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

    ; unrecognized
    jmp .bad_modifier

.modf_s:
    ; get string address
    mov rdi, q[rsi+nx2*8]
    inc nx2

    test rdi, rdi
    j.z .nullstring

.print_string:
    mov ax0, b[rdi]
    test ax0, ax0
    j.z .main_loop

    inc rdi
    call .doput
    jmp .print_string

.modf_c:
    mov ax0, q[rsi+nx2*8]
    inc nx2
    call .doput
    jmp .main_loop

.modf_p:
    mov ax0, '0'
    call .doput
    mov ax0, 'x'
    call .doput
    ; 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
    sub rsp, 80
    mov rdi, rsp

    ; assume modifier already set up ax2
    mov ax0, rsp
    mov ax1, q[rsi+nx2*8]
    call itoa
    inc nx2

.print_itoa_buf:
    mov ax0, b[rdi]

    test ax0, ax0
    add.z rsp, 80
    j.z .main_loop

    inc rdi
    call .doput
    jmp .print_itoa_buf

.modf_percent:
    mov ax0, '%'
    call .doput
    jmp .main_loop

.bad_modifier:
    ; print "%?" to clearly indicate that something is wrong
    mov ax0, '%'
    call .doput

    mov ax0, '?'
    call .doput

    jmp .main_loop

.nullstring:
    ; %s was passed a NULL
    mov ax0, '('
    call .doput

    mov ax0, 'n'
    call .doput

    mov ax0, 'u'
    call .doput

    mov ax0, 'l'
    call .doput

    mov ax0, 'l'
    call .doput

    mov ax0, ')'
    call .doput

    jmp .main_loop

.epilogue:
    mov rax, nx1
    mov rbx, q[rbp-8]
    mov nx0, q[rbp-16]
    mov nx1, q[rbp-24]
    mov nx2, q[rbp-32]
    mov rdi, q[rbp-40]
    mov rsi, q[rbp-48]
    mov nx3, q[rbp-56]
    leave
    dump 1
    ret
;
; prints ax0
;
.doput:
    ; update print count
    inc nx1

    ; 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
    test nx0, nx0
    ret.z

    ; if n>0, decrement n and print
    dec nx0
    call nx3
    
    ; did putc fail?
    cmp rax, 0
    xor.nz nx0, nx0     ; yes, so artificially set n=0

    ret