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@yne yne/av1.c
Created Aug 20, 2019

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av1-like decoder
#include <math.h>
#include <stdio.h>
#define e(a, d) for(a=0;a<d;a++)
int YUV[3][1 << 20], tmpyuv[2048], scratch[166], width;
int p = 0, r = 1;//reader accu
int lumaRatio = 0, satuRatio = 0;//decode default
void read8b() {
int b = getchar();
r = r << 8;
p = (p << 8) + (b < 0 ? 0 : b);
}
int readat(int offset) {
if (r < 256)read8b();
int*spad = scratch + offset * 2;
int F = spad[0] + spad[1] + 2;
int u = r * (spad[0] + 1) / F;
int k = p >= u;
if (k) {
p -= u;
r -= u;
} else r = u;
spad[k]++;
if (F > 63) {
spad[0] /= 2;
spad[1] /= 2;
}
return k;
}
// r = 256 , p = 0+23
int n(int step) {
int a = 0;
while (readat(step + a) == 0)a++;
int b = 1;
while (a--)b = b << 1 | readat(4);
return b - 1;
}
//twice faster with precomputed cos array
void fft(int *S, int Y, const int *T, int Z, int U, int pass, int g) {
int H; e(H, pass) {
int a;e(a, pass) {
int G = 0;
int p;e(p, pass) {
G += T[p * Z + H * U] * lrint(cos(3.1415 / pass * (a + 0.5) * p) * (p ? 1.414 : 1) * 1024);
}
S[a * Y + H * U] = G + (1 << g - 1) >> g;
}
}
}
void decode(int col, int line, int depth) {
int a, k;
if (depth > 5 || depth > 2 && readat(depth - 3)) {
int c = 1 << --depth;
e(a, 4)
decode(col + a % 2 * c, line + a / 2 * c, depth);
return;
}
int size = 1 << depth;
int surface = size * size;
int q = n(73);
int colorspace = 0;e(colorspace, 3) {
int*yuv = YUV[colorspace] + line * width + col;
int isColor = colorspace > 0;
e(a, surface)tmpyuv[a] = 0;
e(a, surface) {
if (readat(61 + depth * 2 + isColor))break;
a += n(5 + isColor * 10);
k = 1 - 2 * readat(3);
tmpyuv[a] = k * (n(25 + (isColor + (a < surface / 8) * 2) * 10) + 1) * (colorspace ? satuRatio : lumaRatio);
}
if (!q) {
int v = 0;
e(a, size) {
v += line ? yuv[a - width ] : 0;
v += col ? yuv[a * width - 1] : 0;
}
*tmpyuv += col && line ? v / 2 : v;
}
fft(tmpyuv + surface, 1, tmpyuv , 1 , size, size, 10);
fft(yuv , width, tmpyuv + surface, size, 1, size, 10 + depth);
if (!q) continue;
int C = q < 17;
int w = C ? 9 - q : q - 25;
e(a, size){
int j;e(j, size) {
int I,J;
e(I, 2) {
int h = a * w + w;
J = h & 7;
h = (h >> 3) + j + I;
k = h < 0;
if (k)h = (h * 8 + w / 2) / w - 2;
h = h < size ? h : size - 1;
tmpyuv[I] = k ^ C ? yuv[h * width - 1] : yuv[-width + h];
}
yuv[C ? j * width + a : a * width + j] += *tmpyuv * (8 - J) + tmpyuv[1] * J + 4 >> 3;
}
}
}
}
void output(int b) {
putchar(b < 0 ? 0 : b > 255 ? 255 : b);
}
int main(int argc) {
read8b();// r = 256 , p = 0+23
int depth = n(5);
width = 1 << depth;
int height = width - n(5);
lumaRatio = n(5);
satuRatio = n(5);
decode(0, 0, depth);
printf("P6 %d %d 255 ", width, height);
for(int a=0,n=height * width;a < n;a++) {
int l = YUV[0][a];//-33..283
int L = YUV[1][a];//-53..43
int M = YUV[2][a];//-79..122
output(l - L + M);
output(l + L);
output(l - L - M);
}
return 0;
}
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