draftng

1 files changed, 120 insertions, 0 deletions

diff --git a/printf.s b/printf.s
new file mode 100644
index 0000000..3bb24ca
--- /dev/null
+++ b/printf.s
@@ -0,0 +1,120 @@
+.include "lib.s"
+
+.macro bufpush
+	cmpq $bufend, %rdi
+	jle 9f
+	stosb
+	9:
+.endm
+
+.globl printf
+printf:
+	prologue
+
+	backup %rax, %rbx, %rcx, %rdx
+	backup %rsi, %rdi
+
+	movq 16(%rbp), %rsi
+	leaq 24(%rbp), %rbx
+	movq $buf, %rdi
+
+.loop:
+	lodsb
+	testb %al, %al
+	jz .loopout
+
+	cmpb $'%, %al
+	jne .append
+
+	lodsb
+	testb %al, %al
+	jz .loopout
+
+	cmpb $'%, %al
+	je .append
+
+	cmpb $'s, %al
+	je .print_string
+
+	cmpb $'d, %al
+	je .print_signed
+
+	cmpb $'u, %al
+	je .print_unsigned
+
+	jmp .loop
+
+.append:
+	bufpush
+	jmp .loop
+
+.print_string:
+	backup %rsi
+
+	movq (%rbx), %rsi
+	addq $8, %rbx
+	jmp 2f
+
+	1: bufpush 
+	2: lodsb
+	testb %al, %al
+	jnz 1b
+
+	restore %rsi
+	jmp .loop
+
+.print_signed:
+	movq (%rbx), %rax
+	addq $8, %rbx
+
+	cmpq $0, %rax
+	jge 1f
+
+	pushq %rax
+	movb $'-, %al
+	bufpush
+	popq %rax
+	negq %rax
+
+	1:
+	movq $10, %rcx
+	call .print_number
+	jmp .loop
+
+.print_unsigned:
+	movq (%rbx), %rax
+	addq $8, %rbx
+
+	movq $10, %rcx
+	call .print_number
+	jmp .loop
+
+.print_number:
+	xorq %rdx, %rdx
+	divq %rcx
+	pushq %rdx
+	testq %rax, %rax
+	jz 1f
+	call .print_number
+	1:
+	popq %rax
+	addq $'0, %rax
+	bufpush
+	ret
+
+.loopout:
+	movq %rdi, %rdx
+	subq $buf, %rdx
+	movq $buf, %rsi
+	movq $STDOUT, %rdi
+	sys write
+
+	restore %rsi, %rdi
+	restore %rax, %rbx, %rcx, %rdx
+
+	leave
+	ret
+
+.bss
+.comm buf, 4096
+.comm bufend, 2