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implement IDCT;
include "sys.m";
include "mpegio.m";
init()
{
}
# Scaled integer implementation.
# inverse two dimensional DCT, Chen-Wang algorithm
# (IEEE ASSP-32, pp. 803-816, Aug. 1984)
# 32-bit integer arithmetic (8 bit coefficients)
# 11 mults, 29 adds per DCT
#
# coefficients extended to 12 bit for IEEE1180-1990
# compliance
W1: con 2841; # 2048*sqrt(2)*cos(1*pi/16)
W2: con 2676; # 2048*sqrt(2)*cos(2*pi/16)
W3: con 2408; # 2048*sqrt(2)*cos(3*pi/16)
W5: con 1609; # 2048*sqrt(2)*cos(5*pi/16)
W6: con 1108; # 2048*sqrt(2)*cos(6*pi/16)
W7: con 565; # 2048*sqrt(2)*cos(7*pi/16)
W1pW7: con 3406; # W1+W7
W1mW7: con 2276; # W1-W7
W3pW5: con 4017; # W3+W5
W3mW5: con 799; # W3-W5
W2pW6: con 3784; # W2+W6
W2mW6: con 1567; # W2-W6
R2: con 181; # 256/sqrt(2)
idct(b: array of int)
{
# transform horizontally
for(y:=0; y<8; y++){
eighty := y<<3;
# if all non-DC components are zero, just propagate the DC term
if(b[eighty+1]==0)
if(b[eighty+2]==0 && b[eighty+3]==0)
if(b[eighty+4]==0 && b[eighty+5]==0)
if(b[eighty+6]==0 && b[eighty+7]==0){
v := b[eighty]<<3;
b[eighty+0] = v;
b[eighty+1] = v;
b[eighty+2] = v;
b[eighty+3] = v;
b[eighty+4] = v;
b[eighty+5] = v;
b[eighty+6] = v;
b[eighty+7] = v;
continue;
}
# prescale
x0 := (b[eighty+0]<<11)+128;
x1 := b[eighty+4]<<11;
x2 := b[eighty+6];
x3 := b[eighty+2];
x4 := b[eighty+1];
x5 := b[eighty+7];
x6 := b[eighty+5];
x7 := b[eighty+3];
# first stage
x8 := W7*(x4+x5);
x4 = x8 + W1mW7*x4;
x5 = x8 - W1pW7*x5;
x8 = W3*(x6+x7);
x6 = x8 - W3mW5*x6;
x7 = x8 - W3pW5*x7;
# second stage
x8 = x0 + x1;
x0 -= x1;
x1 = W6*(x3+x2);
x2 = x1 - W2pW6*x2;
x3 = x1 + W2mW6*x3;
x1 = x4 + x6;
x4 -= x6;
x6 = x5 + x7;
x5 -= x7;
# third stage
x7 = x8 + x3;
x8 -= x3;
x3 = x0 + x2;
x0 -= x2;
x2 = (R2*(x4+x5)+128)>>8;
x4 = (R2*(x4-x5)+128)>>8;
# fourth stage
b[eighty+0] = (x7+x1)>>8;
b[eighty+1] = (x3+x2)>>8;
b[eighty+2] = (x0+x4)>>8;
b[eighty+3] = (x8+x6)>>8;
b[eighty+4] = (x8-x6)>>8;
b[eighty+5] = (x0-x4)>>8;
b[eighty+6] = (x3-x2)>>8;
b[eighty+7] = (x7-x1)>>8;
}
# transform vertically
for(x:=0; x<8; x++){
# if all non-DC components are zero, just propagate the DC term
if(b[x+8*1]==0)
if(b[x+8*2]==0 && b[x+8*3]==0)
if(b[x+8*4]==0 && b[x+8*5]==0)
if(b[x+8*6]==0 && b[x+8*7]==0){
v := (b[x+8*0]+32)>>6;
b[x+8*0] = v;
b[x+8*1] = v;
b[x+8*2] = v;
b[x+8*3] = v;
b[x+8*4] = v;
b[x+8*5] = v;
b[x+8*6] = v;
b[x+8*7] = v;
continue;
}
# prescale
x0 := (b[x+8*0]<<8)+8192;
x1 := b[x+8*4]<<8;
x2 := b[x+8*6];
x3 := b[x+8*2];
x4 := b[x+8*1];
x5 := b[x+8*7];
x6 := b[x+8*5];
x7 := b[x+8*3];
# first stage
x8 := W7*(x4+x5) + 4;
x4 = (x8+W1mW7*x4)>>3;
x5 = (x8-W1pW7*x5)>>3;
x8 = W3*(x6+x7) + 4;
x6 = (x8-W3mW5*x6)>>3;
x7 = (x8-W3pW5*x7)>>3;
# second stage
x8 = x0 + x1;
x0 -= x1;
x1 = W6*(x3+x2) + 4;
x2 = (x1-W2pW6*x2)>>3;
x3 = (x1+W2mW6*x3)>>3;
x1 = x4 + x6;
x4 -= x6;
x6 = x5 + x7;
x5 -= x7;
# third stage
x7 = x8 + x3;
x8 -= x3;
x3 = x0 + x2;
x0 -= x2;
x2 = (R2*(x4+x5)+128)>>8;
x4 = (R2*(x4-x5)+128)>>8;
# fourth stage
b[x+8*0] = (x7+x1)>>14;
b[x+8*1] = (x3+x2)>>14;
b[x+8*2] = (x0+x4)>>14;
b[x+8*3] = (x8+x6)>>14;
b[x+8*4] = (x8-x6)>>14;
b[x+8*5] = (x0-x4)>>14;
b[x+8*6] = (x3-x2)>>14;
b[x+8*7] = (x7-x1)>>14;
}
}
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