view src/hermes/mmx_main.asm @ 3880:74e828c64315 SDL-1.2

Fixed bug #292 I might be on crack here. It looks like SDL_ConvertMono() in src/audio/SDL_audiocvt.c adds the left and right channels of a stereo stream together, and clamps the new mono channel if it would overflow. Shouldn't it be dividing by 2 to average the two sample points instead of clamping? Otherwise the mono sample point's volume doubles in the conversion. This would also make the conversion faster, as it replaces two branches per sample frame with a bitwise shift. --ryan.
author Sam Lantinga <slouken@libsdl.org>
date Sun, 24 Sep 2006 15:45:37 +0000
parents eb4d9d99849b
children 180fa05e98e2
line wrap: on
line source

;
; mmx format converter main loops for HERMES
; Some routines Copyright (c) 1998 Christian Nentwich (c.nentwich@cs.ucl.ac.uk)
; This source code is licensed under the GNU LGPL
; 
; Please refer to the file COPYING.LIB contained in the distribution for
; licensing conditions		
;

BITS 32

%include "common.inc"

SDL_FUNC _ConvertMMX
SDL_FUNC _mmxreturn

SECTION .text
		
;; _ConvertMMX:	 
;; [ESP+8] ConverterInfo*
;; --------------------------------------------------------------------------
;; ConverterInfo (ebp+..)
;;   0:	void *s_pixels
;;   4:	int s_width
;;   8:	int s_height
;;  12:	int s_add
;;  16:	void *d_pixels
;;  20:	int d_width
;;  24:	int d_height
;;  28:	int d_add
;;  32:	void (*converter_function)() 
;;  36: int32 *lookup
	
_ConvertMMX:
	push ebp
	mov ebp,esp

; Save the registers used by the blitters, necessary for optimized code
	pusha

	mov eax,[ebp+8]

        cmp dword [eax+4],BYTE 0
	je endconvert
	
	mov ebp,eax
	
	mov esi,[ebp+0]
	mov edi,[ebp+16]
	
y_loop:	
	mov ecx,[ebp+4]

	jmp [ebp+32]

_mmxreturn:	
	add esi,[ebp+12]
	add edi,[ebp+28]
	
	dec dword  [ebp+8]
	jnz y_loop

	
; Restore the registers used by the blitters, necessary for optimized code
	popa

	pop ebp

endconvert:
	emms
	
	ret		

%ifidn __OUTPUT_FORMAT__,elf
section .note.GNU-stack noalloc noexec nowrite progbits
%endif