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77 lines
1.4 KiB
ArmAsm
77 lines
1.4 KiB
ArmAsm
;
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; int printf (const char* Format, ...);
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;
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; Ullrich von Bassewitz, 1.12.2000
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;
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.export _printf
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.import _stdout, pushax, addysp, _vfprintf
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.importzp sp, ptr1
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.macpack generic
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; ----------------------------------------------------------------------------
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; Data
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.bss
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ParamSize: .res 1 ; Number of parameter bytes
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; ----------------------------------------------------------------------------
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; Code
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.code
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_printf:
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sty ParamSize ; Number of param bytes passed in Y
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; We are using a (hopefully) clever trick here to reduce code size. On entry,
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; the stack pointer points to the last pushed parameter of the variable
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; parameter list. Adding the number of parameter bytes, would result in a
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; pointer that points *after* the Format parameter.
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; Since we have to push stdout anyway, we will do that here, so
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;
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; * we will save the subtraction of 2 (__fixargs__) later
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; * we will have the address of the Format parameter which needs to
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; be pushed next.
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;
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lda _stdout
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ldx _stdout+1
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jsr pushax
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; Now calculate the va_list pointer, which does points to Format
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lda sp
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ldx sp+1
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add ParamSize
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bcc @L1
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inx
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@L1: sta ptr1
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stx ptr1+1
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; Push Format
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ldy #1
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lda (ptr1),y
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tax
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dey
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lda (ptr1),y
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jsr pushax
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; Load va_list (last and __fastcall__ parameter to vfprintf)
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lda ptr1
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ldx ptr1+1
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; Call vfprintf
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jsr _vfprintf
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; Cleanup the stack. We will return what we got from vfprintf
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ldy ParamSize
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jmp addysp
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