Category : C Source Code
Archive   : IMDSRC78.ZIP
Filename : RESCALE.ASM

;
; RESCALE.ASM - routines to perform various precision conversion on arrays
;
; Written 2/91 by A. Warnock, ST Systems Corp. for use with IMDISP
;-------------------------------------------------------------------------
;
; b2w - scales 8-bit unsigned integer data to 16 bits
; from C:
; b2w (in8, out16, num_pix);
;
;-------------------------------------------------------------------------

.MODEL LARGE
.CODE
PUBLIC _b2w
_b2w PROC

push bp ; Entry sequence - save old bp
mov bp, sp ; set stackframe pointer

mov dx, [bp+6] ; move in8 address to dx
mov bx, [bp+10] ; move out16 address to bx
mov cx, [bp+14] ; move count to cx

b2wtop: mov si, dx ; stash the 8-bit array address
mov al, [si] ; grab the byte value from the array
cbw ; convert to word value with sign extend
xor ah, ah ; clear the high byte (was unsigned)
mov [bx], ax ; and shove the result into out16
;
; bump the pointers and the count
;
inc dx ; point to next byte in in8
add bx,2 ; point to next word in out16 - 2 bytes
dec cx ; take 1 from the count
jcxz b2wret ; bail out if cx=0
jmp b2wtop ; or else do the next value

b2wret:
pop bp ; Exit sequence - restore old bp
ret ; Return

_b2w ENDP

;-------------------------------------------------------------------------
;
; w2b - scales 16-bit integer data to 8 bit unsigned
; from C:
; w2b (in16, out8, num_pix);
;
;-------------------------------------------------------------------------

PUBLIC _w2b
_w2b PROC

push bp ; Entry sequence - save old bp
mov bp, sp ; set stackframe pointer

mov dx, [bp+6] ; move in16 address to dx
mov bx, [bp+10] ; move out8 address to bx
mov cx, [bp+14] ; move count to cx

w2btop: mov si, dx ; stash the 16-bit array address
mov ax, [si] ; grab the word value from the array
mov di, bx ; stash the 8-bit array address
mov [di], ah ; put high word of input into output address
;
; bump the pointers and the count
;
add dx,2 ; point to next word in in16
inc bx ; point to next byte in out8
dec cx ; take 1 from the count
jcxz w2bret ; bail out if cx=0
jmp w2btop ; or else do the next value

w2bret:
pop bp ; Exit sequence - restore old bp
ret ; Return

_w2b ENDP

END