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/*
Colour conversion routines (RGB <-> YUV) in x86 assembly
 
(C) 2000 Nemosoft Unv.    nemosoft@smcc.demon.nl
   
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.   

*/


/* The ccvt_* functions always start with width and height, so these
   parameters are in 8(%ebp) and 12 (%ebp). The other parameters can be
   2 to 4 pointers, and one of these combinations:
   *src, *dst
   *srcy, *srcu, *srv, *dst
   *src, *dsty, *dstu, *dstv
 */   

#define __ASSEMBLY__
#include <linux/linkage.h>

#define Width   8(%ebp)
#define Height 12(%ebp)

/* 2 parameters, 1 in, 1 out */
#define Src2 16(%ebp)
#define Dst2 20(%ebp)

/* 4 parameters, 3 in, 1 out */
#define SrcY 16(%ebp)
#define SrcU 20(%ebp)
#define SrcV 24(%ebp)
#define Dst4 28(%ebp)

/* 4 parameters, 1 in, 3 out */
#define Src4 16(%ebp)
#define DstY 20(%ebp)
#define DstU 24(%ebp)
#define DstV 28(%ebp)

/* This buffer space used to be staticly allocted, but this is going to
   give problems with multiple cams (though I have yet to see it).
   Therefor, we reserve at least 64 + 8 = 72 bytes on the stack with 
   `enter'.
 */

#define PixelBuffer -64(%ebp)
#define Uptr        -68(%ebp)
#define Vptr        -72(%ebp)

        .text

/* This function will load the src and destination pointers, including
   Uptr/Vptr when necessary, and test the width/height parameters.
   - %esi will be set to Src or SrcY
   - %edi will be set to Dst or DstY
   the carry flag will be set if any of these tests fail. 
   It assumes %ebp has been set.
 */
/* 2 parameters, src & dst */
test_param_2:
        mov Src2, %esi
        mov Dst2, %edi
        
        cmp $0, %esi            # NULL pointers?
        je param_fail
        cmp $0, %edi
        je param_fail

        jmp test_width_height

/* 3 inputs, 1 output */
test_param_31:
        mov Dst4, %edi          # NULL pointers
        cmp $0, %edi
        je param_fail
        
        mov SrcV, %esi
        cmp $0, %esi
        je param_fail
        mov %esi, Vptr

        mov SrcU, %esi
        cmp $0, %esi
        je param_fail
        mov %esi, Uptr
        
        mov SrcY, %esi
        cmp $0, %esi
        je param_fail
        
        jmp test_width_height

/* 1 input, 3 output */ 
test_param_13:
        mov Src4, %esi          # NULL pointers
        cmp $0, %esi
        je param_fail
        
        mov DstV, %edi
        cmp $0, %edi
        je param_fail
        mov %edi, Vptr
        
        mov DstU, %edi
        cmp $0, %edi
        je param_fail
        mov %edi, Uptr
        
        mov DstY, %edi
        cmp $0, %edi
        je param_fail
        
        jmp test_width_height
        
        nop

test_width_height:
        cmpl $0, Width
        jbe param_fail
        testl $3, Width         # multiple of 4?
        jnz param_fail          # Nope...

        cmp $0, Height          # check illegal height
        jbe param_fail
        testl $1, Height        # Odd no. of lines?
        jnz param_fail          # Aye

        /* fall through */

/* exit points */
param_ok:
        clc                     # Success: clear carry
        ret

param_fail:
        stc                     # Fail: set carry
        ret



# This will fill PixelBuffer with 4 grey scale pixels (Y)
# In:           %eax = Value (Y3Y2Y1Y0)
# Out:
# Modifies:     %ecx (-4)
# Destroys:     %edx
expand_4_y:
        mov %eax, %edx          # Keep in edx (we need eax)
        lea PixelBuffer, %edi   
        
0:      # This code is executed 4 times
        movzbl %dl, %eax        # move, zero extending byte-to-long
        shl $8, %eax            # 8 digit precision
        
        stosl                   # Expand into PixelBuffer
        stosl
        stosl
        add $4, %edi            # Skip alpha

        shr $8, %edx            # next Y

        dec %ecx
        test $3, %ecx
        jnz 0b

        ret                     # from expand_4_y
        
# This will add the color factors to the (grey) values in PixelBuffer
# In:           %ebx (U1U0V1V0)
# Out:
# Modifies:
# Destroys:     %edi, %ebx, %eax, %edx
expand_4_uv:
        lea PixelBuffer, %edi   # reset pointer

        # V0
        sub $128, %bl
        movsbl %bl, %eax
        mov $359, %edx          # Vr
        mul %edx
        add %eax, 0x00(%edi)
        add %eax, 0x10(%edi)
        
        movsbl %bl, %eax
        mov $183, %edx          # Vg
        mul %edx
        sub %eax, 0x04(%edi)
        sub %eax, 0x14(%edi)
        
        # V1
        sub $128, %bh
        movsbl %bh, %eax
        mov $359, %edx          # Vr
        mul %edx
        add %eax, 0x20(%edi)
        add %eax, 0x30(%edi)
        
        movsbl %bh, %eax
        mov $183, %edx          # Vg
        mul %edx
        sub %eax, 0x24(%edi)
        sub %eax, 0x34(%edi)
        
        # U0
        bswap %ebx              # Get U values in lower half
        sub $128, %bh
        movsbl %bh, %eax
        mov $88, %edx           # Ug
        mul %edx
        sub %eax, 0x04(%edi)
        sub %eax, 0x14(%edi)

        movsbl %bh, %eax
        mov $454, %edx          # Ub
        mul %edx
        add %eax, 0x08(%edi)
        add %eax, 0x18(%edi)
        
        # U1
        sub $128, %bl
        movsbl %bl, %eax
        mov $88, %edx           # Ug
        mul %edx
        sub %eax, 0x24(%edi)
        sub %eax, 0x34(%edi)
        
        movsbl %bl, %eax
        mov $454, %edx          # Ub
        mul %edx
        add %eax, 0x28(%edi)
        add %eax, 0x38(%edi)
        ret                     # expand_4_uv


/* This function expands 4 420i pixels into PixelBuffer */
do_four_yuvi:
        push %edi

        lodsl                   # 4 bytes at a time
        
        call expand_4_y
        
        # now do UV values. on even lines, Y is followed by U values; on 
        # odd lines V values follow. The U and V values are always pushed
        # on the stack in this order:
        # U V
        
        # First, calculate offset per line (1.5 * width)
        mov Width, %ebx # width
        shl %ebx                # 2 *
        add Width, %ebx # 3 * 
        shr %ebx                # 1.5 *

        # even or odd lines     
        testl $1, Height
        jz 2f

        # odd line; we are at V data, but do U data first
        neg %ebx                # make ebx offset negative
        mov (%esi,%ebx),%ax     # U
        push %ax
        lodsw                   # V
        push %ax
        jmp 3f  
        
2:      # even line
        lodsw                   # U
        push %ax
        sub $2, %ebx
        mov (%esi,%ebx), %ax    # V
        push %ax

3:      # Okay, so we now have the U and V values... expand into PixelBuffer

        pop %ebx
        call expand_4_uv

        pop %edi
        ret                     # from do_four_yuvi


# Do four pixels, in planar format
do_four_yuvp:
        push %edi

        # The first part is the same as for interlaced (4 bytes Y)
        lodsl                   # 4 bytes at a time
        call expand_4_y
        
        # now gather U and V values... 
        mov Uptr, %ebx          # Use Uptr/Vptr
        mov (%ebx), %ax
        push %ax
        add $2, %ebx
        mov %ebx, Uptr

        mov Vptr, %ebx
        mov (%ebx), %ax
        push %ax
        add $2, %ebx
        mov %ebx, Vptr
        
        pop %ebx
        call expand_4_uv
        
        pop %edi
        ret


# Do four pixels, in yuyv interlaced format
do_four_yuyv:
        push %edi

        lodsl                   # v0y1u0y0
        mov %eax, %ebx
        bswap %ebx              # y0u0y1v0
        mov %bh, %ah            # v0y1y1y0
        and $0x00ff00ff, %ebx   # __u0__v0
        push %ax                # y1y0

        lodsl                   # v1y3u1y2      # mix register instructions
        mov %eax, %edx                          # so CPU pipeline doesnt stall
        rol $16, %eax           # u1y2v1y3      
        mov %dl, %dh            # v1y3y2y2
        and $0xff00ff00, %eax   # u1__v1__
        mov $0, %dl             # v1y3y2__
        or %eax, %ebx           # u1u0v1v0
        shl $8, %edx            # y3y2____
        pop %dx                 # y3y2y1y0
        mov %edx, %eax
        call expand_4_y
        call expand_4_uv
        
        pop %edi
        ret

limit_pixels:
        # Limit all values in PixelBuffer
        push %esi
        push %edi
        push %ecx
        lea PixelBuffer, %esi
        mov %esi, %edi
        mov $16, %ecx
0:      lodsl
        cmp $0, %eax            # this would have been a perfect spot for CMOVxx instructions...
        jl 2f                   #  except they only work on Pentium Pro processors,
        cmp $0xff00, %eax       #  and not even all of them
        jg 3f
        add $4, %edi            # no use for stosl here
        loop 0b
        jmp 9f
2:      mov $0, %eax
        stosl
        loop 0b
        jmp 9f
3:      mov $0xff00, %eax
        stosl
        loop 0b
        jmp 9f

9:      pop %ecx
        pop %edi
        pop %esi
        ret                     # from limit_pixels

/* Copy RGB values from PixelBuffer into destination buffer, 4 bytes
   with alpha 
 */

/* Push 3 pixel (12 bytes), in correct order */
push_rgb24:
        push %ecx
        push %esi
        lea PixelBuffer, %esi
        mov $4, %ecx
0:      lodsl
        shr $8, %eax
        mov %al, (%edi)         # Red
        lodsl
        shr $8, %eax
        mov %al, 1(%edi)        # Green
        lodsl
        shr $8, %eax
        mov %al, 2(%edi)        # Blue
        add $3, %edi
        lodsl                   # dummy
        loop 0b
        pop %esi
        pop %ecx
        ret

/* Push 3 pixels (12 bytes), in wrong order */
push_bgr24:
        push %ecx
        push %esi
        lea PixelBuffer, %esi
        mov $4, %ecx
0:      lodsl
        shr $8, %eax
        mov %al, 2(%edi)        # Red
        lodsl
        shr $8, %eax
        mov %al, 1(%edi)        # Green
        lodsl
        shr $8, %eax
        mov %al, (%edi)         # Blue
        add $3, %edi
        lodsl                   # dummy
        loop 0b
        pop %esi
        pop %ecx
        ret

/* The simplest format: push 4 bytes, RGBa */
push_rgb32:
        push %ecx
        push %esi
        mov $16, %ecx
        lea PixelBuffer, %esi
0:      lodsl                   # red
        shr $8, %eax            # 8 bit precision
        stosb
        loop 0b
        pop %esi
        pop %ecx
        ret


/* Gosh. Would you believe it. They even made this format... (Qt 2.*) */
push_bgr32:
        # copy all 4 values to output buffer
        push %ecx
        push %esi
        mov $4, %ecx
        lea PixelBuffer, %esi
0:      lodsl                   # red
        shr $8, %eax            # 8 bit precision
        mov %al, 2(%edi)
        lodsl                   # green
        shr $8, %eax
        mov %al, 1(%edi)
        lodsl                   # blue
        shr $8, %eax
        mov %al, (%edi)
        add $4, %edi
        lodsl                   # dummy
        loop 0b 
        pop %esi
        pop %ecx
        ret

/*************************************/

/* Functions to go from YUV interlaced formats to RGB */

/* Go from interlaced to RGB, red first */

ENTRY(ccvt_420i_rgb24)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f
        
0:      mov Width, %ecx         # width
1:      call do_four_yuvi
        call limit_pixels
        call push_rgb24
                        
        cmp $0, %ecx
        jnz 1b                  # end of line?
        decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* Go from interlaced to BGR, blue first */

ENTRY(ccvt_420i_bgr24)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f
        
0:      mov Width, %ecx # width
1:      call do_four_yuvi
        call limit_pixels
        call push_bgr24
                        
        cmp $0, %ecx
        jnz 1b                  # end of line?
        decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret


/* From interlaced to RGBa */

ENTRY(ccvt_420i_rgb32)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f

0:      mov Width, %ecx         # width
1:      call do_four_yuvi
        call limit_pixels
        call push_rgb32
                
        cmp $0, %ecx            # end of line?
        jnz 1b
        decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* Guess what? Go from interlaced to BGRa */

ENTRY(ccvt_420i_bgr32)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f

0:      mov Width, %ecx         # width
1:      call do_four_yuvi
        call limit_pixels
        call push_bgr32
                
        cmp $0, %ecx            # end of line?
        jnz 1b
        decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret




/* From YUYV to RGBa */

ENTRY(ccvt_yuyv_rgb32)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f
        
0:      mov Width, %ecx         # width
1:      call do_four_yuyv
        call limit_pixels
        call push_rgb32
                
        cmp $0, %ecx            # end of line?
        jnz 1b

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* From YUYV to BGRa */
ENTRY(ccvt_yuyv_bgr32)
        enter $72, $0           # no extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f
        
        # YUYV -> RGBa RGBa

0:      mov Width, %ecx         # width
1:      call do_four_yuyv
        call limit_pixels
        call push_bgr32
                
        cmp $0, %ecx            # end of line?
        jnz 1b

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret




/* Planar to RGBa */

ENTRY(ccvt_420p_rgb32)
        enter $72, $0
        push %ebx
        push %esi
        push %edi
        
        call test_param_31
        jc 9f

        mov Width, %eax         # width
        mull Height             # * height
        mov SrcU, %eax          # Copy U/V pointers
        mov %eax, Uptr
        mov SrcV, %eax
        mov %eax, Vptr

0:      mov Width, %ecx         # width
1:      call do_four_yuvp
        call limit_pixels
        call push_rgb32 
                
        cmp $0, %ecx            # end of line?
        jnz 1b

        testl $1, Height        # odd/even line
        jnz 8f
        
        mov Width, %eax         # Even: rewind U/V pointers
        shr %eax
        sub %eax, Uptr
        sub %eax, Vptr

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* Okay... eventually, you end up with a very complete set of conversion
   routines. I just wished things were a bit simpler. */

/* Planar to RGB */

ENTRY(ccvt_420p_rgb24)
        enter $72, $0
        push %ebx
        push %esi
        push %edi
        
        call test_param_31
        jc 9f

        mov Width, %eax         # width
        mull Height             # * height
        mov SrcU, %eax          # Copy U/V pointers
        mov %eax, Uptr
        mov SrcV, %eax
        mov %eax, Vptr

0:      mov Width, %ecx         # width
1:      call do_four_yuvp
        call limit_pixels
        call push_rgb24 
                
        cmp $0, %ecx            # end of line?
        jnz 1b

        testl $1, Height        # odd/even line
        jnz 8f
        
        mov Width, %eax         # Even: rewind U/V pointers
        shr %eax
        sub %eax, Uptr
        sub %eax, Vptr

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* Planar to RGB */

ENTRY(ccvt_420p_bgr24)
        enter $72, $0
        push %ebx
        push %esi
        push %edi
        
        call test_param_31
        jc 9f

        mov Width, %eax         # width
        mull Height             # * height
        mov SrcU, %eax          # Copy U/V pointers
        mov %eax, Uptr
        mov SrcV, %eax
        mov %eax, Vptr

0:      mov Width, %ecx         # width
1:      call do_four_yuvp
        call limit_pixels
        call push_bgr24 
                
        cmp $0, %ecx            # end of line?
        jnz 1b

        testl $1, Height        # odd/even line
        jnz 8f
        
        mov Width, %eax         # Even: rewind U/V pointers
        shr %eax
        sub %eax, Uptr
        sub %eax, Vptr

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret

/* Okay... eventually, you end up with a very complete set of conversion
   routines. I just wished things were a bit simpler. */

ENTRY(ccvt_420p_bgr32)
        enter $72, $0
        push %ebx
        push %esi
        push %edi
        
        call test_param_31
        jc 9f
        
        mov Width, %eax         # width
        mull Height             # * height
        mov SrcU, %eax          # Copy U/V pointers
        mov %eax, Uptr
        mov SrcV, %eax
        mov %eax, Vptr

0:      mov Width, %ecx         # width
1:      call do_four_yuvp
        call limit_pixels
        call push_bgr32
                
        cmp $0, %ecx            # end of line?
        jnz 1b

        testl $1, Height        # odd/even line
        jnz 8f
        
        mov Width, %eax         # Even: rewind U/V pointers
        shr %eax
        sub %eax, Uptr
        sub %eax, Vptr

8:      decl Height             # yes; decrement line counter
        jnz 0b

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret




/* Go from RGB (red first) to 4:2:0 planar.
 * Note: this requires decimation of the U/V space by 2 in both directions 
 * Also, a matrix multiply would be QUITE convenient...

   This is the matrix:
     (Y )   ( 77  150   29)   (R)
     (Cb) = (-43  -85  128) * (G)
     (Cr)   (128 -107  -21)   (B)
 */

ENTRY(ccvt_rgb24_420p)
        enter $96, $0           # 24 bytes extra stack, no stackframes
        push %ebx               #  -76: line width in bytes
        push %esi               #  -80: height (copy)
        push %edi               #  -84: width (copy)
                                #  -88: red factor
                                #  -92: green factor
                                #  -96: blue factor
        call test_param_13
        jc 9f

        mov Width, %eax
        shl %eax
        add Width, %eax         # 3 * width = line increment
        mov %eax, -76(%ebp)

        mov Height, %eax
        mov %eax, -80(%ebp)     # copy height into stackframe
        
        /*
          This is a bit complicated... since U/V decimation is taking 
          place both in horizontal and vertical direction, we have to
          process 2 lines in parallel. Also, 2 adjacent pixels are
          considered. We average the U/V values over these 4 pixels
          (of course, we could have just taken the U/V value of the first
          pixel and be done with it, but that's not how we do things around
          here)
         */
        
        # 1st pass: Y values. Set factors       
        movl $77 , -88(%ebp)    # 0.299
        movl $150, -92(%ebp)    # 0.587
        movl $29 , -96(%ebp)    # 0.114

0:      mov Width, %ecx         # width
1:      xor %ebx, %ebx          # 0
        call rgb_multiply
        shr $8, %ebx            # divide by 256 (no need for limitor, since 77 + 150 + 29 = 256)
        mov %bl, %al
        stosb                   # store it into Y buffer
        
        dec %ecx                # end of line?
        jnz 1b
        decl -80(%ebp)          # end of image?
        jnz 0b

        # Okay, now the U/V pointers... 
        # The following code is passed twice, with different factors
        # Note that the %esi pointer jumps around quite a bit

        # factors for U
        movl $-43, -88(%ebp)    # -0.1687
        movl $-85, -92(%ebp)    # -0.3313
        movl $128, -96(%ebp)    # 0.5
        mov DstU, %edi          # Set %edi register now
                
7:      mov Src4, %esi          # Rewind source pointer

        mov Height, %eax        # height
        shr %eax                #  / 2
        mov %eax, -80(%ebp)     #   copy

2:      mov Width, %eax         # width
        shr %eax                #  / 2
        mov %eax, -84(%ebp)     #   copy

3:      xor %ebx, %ebx          # 0
        mov $4, %ecx            # average over 4 pixels

4:      call rgb_multiply

        dec %ecx
        jz 5f                   # done?
        cmp $2, %ecx            # 3rd pixel.. move %esi to next line, with offset
        jne 4b
        sub $6, %esi            # backup to where we started
        add -76(%ebp), %esi     # add line increment
        jmp 4b

5:      # okay, 4 pixels done... 
        sub -76(%ebp), %esi     # Get %esi back to its proper place

        add $0x20000, %ebx      # add 0.5 factor
        shr $10, %ebx           # Divide by 4 * 256
        mov %bl, %al
        stosb                   # store it!

        decl -84(%ebp)          # end of line?
        jnz 3b
        add -76(%ebp), %esi     # %esi to next line (actually, 2 lines further)
        decl -80(%ebp)          # end of image?
        jnz 2b

        # check if 3rd pass has been done
        cmpl $128, -88(%ebp)
        je 9f                   # Done!
        # Set factors for V pass
        movl $128 , -88(%ebp)   # 0.5
        movl $-107, -92(%ebp)   # -0.4187
        movl $-21 , -96(%ebp)   # -0.0813
        mov DstV, %edi          # %edi to V buffer
        jmp 7b                  # "Do it to me one more time..."

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret




ENTRY(ccvt_bgr24_420p)
        enter $96, $0           # 24 bytes extra stack, no stackframes
        push %ebx               #   -4: line width in bytes
        push %esi               #   -8: height (copy)
        push %edi               #  -12: width (copy)
                                #  -16: red factor
                                #  -20: green factor
                                #  -24: blue factor
        call test_param_13
        jc 9f

        /* No surprise, this code looks just like rgb24_420p, but with swapped factors */
         
        mov Width, %eax
        shl %eax
        add Width, %eax         # 3 * width = line increment
        mov %eax, -76(%ebp)

        mov Height, %eax
        mov %eax, -80(%ebp)     # copy height into stackframe
        
        # 1st pass: Y values. Set factors       
        movl $29 , -88(%ebp)    # 0.114
        movl $150, -92(%ebp)    # 0.587
        movl $77 , -96(%ebp)    # 0.299

0:      mov Width, %ecx         # width
1:      xor %ebx, %ebx          # 0
        call rgb_multiply
        shr $8, %ebx            # divide by 256 (no need for limitor, since 77 + 150 + 29 = 256)
        mov %bl, %al
        stosb                   # store it into Y buffer
        
        dec %ecx                # end of line?
        jnz 1b
        decl -80(%ebp)          # end of image?
        jnz 0b

        # Okay, now the U/V pointers... 
        # The following code is passed twice, with different factors
        # Note that the %esi pointer jumps around quite a bit

        # factors for U
        movl $123, -88(%ebp)    #  0.5
        movl $-85, -92(%ebp)    # -0.3313
        movl $-43, -96(%ebp)    # -0.1687
        mov DstU, %edi          # Set %edi register now
                
7:      mov Src4, %esi          # Rewind source pointer

        mov Height, %eax        # height
        shr %eax                #  / 2
        mov %eax, -80(%ebp)     #   copy

2:      mov Width, %eax         # width
        shr %eax                #  / 2
        mov %eax, -84(%ebp)     #   copy

3:      xor %ebx, %ebx          # 0
        mov $4, %ecx            # average over 4 pixels

4:      call rgb_multiply

        dec %ecx
        jz 5f                   # done?
        cmp $2, %ecx            # 3rd pixel.. move %esi to next line, with offset
        jne 4b
        sub $6, %esi            # backup to where we started
        add -76(%ebp), %esi     # add line increment
        jmp 4b

5:      # okay, 4 pixels done... 
        sub -76(%ebp), %esi     # Get %esi back to its proper place

        add $0x20000, %ebx      # add 0.5 factor
        shr $10, %ebx           # Divide by 4 * 256
        mov %bl, %al
        stosb                   # store it!

        decl -84(%ebp)          # end of line?
        jnz 3b
        add -76(%ebp), %esi     # %esi to next line (actually, 2 lines further)
        decl -80(%ebp)          # end of image?
        jnz 2b

        # check if 3rd pass has been done
        cmpl $-21, -88(%ebp)
        je 9f                   # Done!
        # Set factors for V pass
        movl $-21 , -88(%ebp)   # -0.0813
        movl $-107, -92(%ebp)   # -0.4187
        movl $128 , -96(%ebp)   #  0.5
        mov DstV, %edi          # %edi to V buffer
        jmp 7b                  # "Do it to me one more time..."

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret


/* RGB-to-YUV helper functions */

rgb_multiply:
        # do one RGB vector multiplication; its assumed the RGB factors
        # are set on the stack. The data is accumulated in ebx.
        lodsb                   # red byte
        and $0xff, %eax
        mov -88(%ebp), %edx     # red factor
        mul %edx
        add %eax, %ebx
        lodsb                   # green byte
        and $0xff, %eax
        mov -92(%ebp), %edx     # green factor
        mul %edx
        add %eax, %ebx
        lodsb                   # blue byte
        and $0xff, %eax
        mov -96(%ebp), %edx     # blue factor
        mul %edx
        add %eax, %ebx          # ebx now contains sum
        ret



/**************************************************************************/


/* Go from 'interlaced' (YYYY UU/VV) format to planar */

ENTRY(ccvt_420i_420p)
        enter $76, $0           # 4 bytes extra space, no stackframes
        push %ebx               # -4: width / 4
        push %esi
        push %edi

        call test_param_13
        jc 9f

        # Okay, this is fairly easy... we first grab the Y values (4 bytes
        #  at a time), then rewind and do the U values, and repeat for V.
        #  This leaves us with a nice planar format

        mov Width, %eax
        shr %eax
        shr %eax                # width / 4
        mov %eax, -76(%ebp)     # Store

        # Y
        mov Height, %edx        # line counter
0:      mov -76(%ebp), %ecx
1:      lodsl                   # get 4 bytes...
        stosl                   # ...push 4 bytes
        add $2, %esi            # Skip U or V
        loop 1b
        dec %edx
        jnz 0b

        # U
        mov Src4, %esi          # rewind source pointer
        mov DstU, %edi
        add $4, %esi            # set to U 
        mov Height, %edx
        shr %edx                # height / 2
        mov Width, %ebx
        shl %ebx
        add Width, %ebx
        shr %ebx                # Width * 1.5 (line offset)

2:      mov -76(%ebp), %ecx     # width / 4
3:      lodsw                   # 2 bytes at a time
        stosw
        add $4, %esi            # skip Y
        loop 3b
        add %ebx, %esi          # Skip line (U is on even lines)
        dec %edx
        jnz 2b
        
        # V
        mov Src4, %esi          # rewind, set to V in first odd line
        add $4, %esi
        add %ebx, %esi          # register re-use; no compiler can beat that :)
        mov DstV, %edi          # V ptr
        mov Height, %edx
        shr %edx                # height / 2
        
4:      mov -76(%ebp), %ecx     # Get width/4
5:      lodsw
        stosw
        add $4, %esi            # Skip Y
        loop 5b
        add %ebx, %esi          # Skip line (V is on odd lines)
        dec %edx
        jnz 4b
        
        /* That's it! */
        
9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret


/* Go from 4:2:0 interlaced to 'normal' YUYV */

ENTRY(ccvt_420i_yuyv)
        enter $80, $0           # 8 bytes extra space, no stackframes
        push %ebx
        push %esi
        push %edi

        call test_param_2
        jc 9f
        
        mov Width, %ecx         # -4: width / 4 = no. loops per line
        shr %ecx
        shr %ecx
        mov %ecx, -76(%ebp)

        mov Width, %ebx         # -8: width * 1.5 = line offset
        shl %ebx
        add Width, %ebx
        shr %ebx
        mov %ebx, -80(%ebp)
        
        # Okay, this requires a bit of byte shuffling... we go from
        #  YYYY UU
        #  YYYY VV
        # to
        #  YUYV YUYV
        #  YUYV YUYV
        # which indeed takes up more space

        # 
        
0:      mov -76(%ebp), %ecx

1:      lodsl                   # 4 Y in eax
        testl $1, Height        # even or odd line?
        jnz 2f
        
        # Even
        mov -80(%ebp), %ebx
        mov (%ebx, %esi), %dx   # 16 bits V 
        shl $16, %edx           # store in high word
        mov (%esi), %dx         # 16 bits U 
        add $2, %esi
        jmp 3f
        
2:      # Odd
        mov -80(%ebp), %ebx
        neg %ebx                # negative offset
        mov (%esi), %dx         # 16 bits V
        shl $16, %edx           # store in high word
        mov (%ebx, %esi), %dx   # 16 bits U
        add $2, %esi

3:      # eax = Y3Y2Y1Y0, edx = V1V0U1U0, ebx is free
        push %eax

        movzbl %al, %ebx        # ______y0
        and $0xFF00, %eax       # ____y1__
        shl $8, %eax            # __y1____
        or %ebx, %eax           # __y1__y0
        mov %edx, %ebx          # v1v0u1u0
        shl $8, %ebx            # v0u1u0__
        and $0xff00ff00, %ebx   # v0__u0__
        or %ebx, %eax           # v0y1u0y0
        stosl   

        pop %eax                # y3y2y1y0
        # Second half
        shr $8, %eax            # __y3y2y1
        shr $8, %ax             # __y3__y2
        and $0xff00ff00, %edx   # v1__u1__
        or %edx, %eax           # v1y3u1y2
        stosl
        
        loop 1b


        decl Height             # height--
        jnz 0b
        # Done

9:      pop %edi
        pop %esi
        pop %ebx
        leave
        ret