[FFmpeg-devel] [PATCH 3/3] avcodec/sheervideo: Avoid code duplication when creating VLC tables

[Andreas Rheinhardt]

Paul B Mahol:
> On Sat, Oct 10, 2020 at 08:59:56PM +0200, Andreas Rheinhardt wrote:
>> The SheerVideo decoder uses two VLC tables and these are in turn created
>> from structures (called SheerTable) that are naturally paired. This
>> commit unifies these pairs of SheerTables to arrays and unifies creating
>> the VLC tables.
> 
> patch-set should be fine if all variant of files are still decoded fine
> after this set applied.
> 
I tested all files from
https://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket492/ which
unfortunately don't cover all variants and they decode the same. Given
that the new tables have been created automatically* I am confident that
I made no errors.

- Andreas

*: using this small program:


#include <stdio.h>
#include <stdint.h>
#include "sheervideodata.h"

void test(const char *name, const uint8_t *table, int size)
{
    int last = 0;
    int descending = 0;
    int counts[2][16] = { { 0 } }, count = 0;

    for (int i = 0; i < size; i++) {
        int cur = table[i];

        if (descending) {
            if (last < cur) {
                printf("Table %s not according to expectations at index
%d.\n",
                       name, i);
                return;
            }
        } else if (last > cur)
            descending = 1;
        if (cur > 16 || cur <= 0) {
            printf("Element %d of table %s out of range.\n", i, name);
            return;
        }
        counts[descending][cur - 1]++;
        last = cur;
    }
    if (!descending) {
        printf("Still ascending.\n");
        return;
    }
    if (counts[1][15]) {
        printf("Strange");
        return;
    }
    for (int i = 0; i < 16; i++)
        count += counts[0][i] + counts[1][i];

    if (count != size) {
        printf("Strange2");
        return;
    }
    if (counts[0][15] > UINT16_MAX) {
        printf("Strange3");
        return;
    }
    printf("static const SheerTable %s = {\n    {", name);
    for (int i = 0; i < 15; i++)
        printf("%3d,", counts[0][i]);
    printf("\n     ");
    for (int i = 0; i < 14; i++)
        printf("%3d,", counts[1][14 - i]);
    printf("%3d }, %d\n };\n\n", counts[1][0], counts[0][15]);
}

#define test(table, size) test(#table, table, size)

int main()
{
    test(l_r_rgb,     256);
    test(l_g_rgb,     256);
    test(l_r_rgbi,    256);
    test(l_g_rgbi,    256);
    test(l_y_ybr,     256);
    test(l_u_ybr,     256);
    test(l_y_ybyr,    256);
    test(l_u_ybyr,    256);
    test(l_y_byry,    256);
    test(l_u_byry,    256);
    test(l_y_ybr10i, 1024);
    test(l_y_ybr10,  1024);
    test(l_u_ybr10i, 1024);
    test(l_u_ybr10,  1024);
    test(l_r_rgbx,   1024);
    test(l_g_rgbx,   1024);
    test(l_y_yry10,  1024);
    test(l_u_yry10,  1024);
    test(l_y_yry10i, 1024);
    test(l_u_yry10i, 1024);
    test(l_y_ybri,    256);
    test(l_u_ybri,    256);
    test(l_y_byryi,   256);
    test(l_u_byryi,   256);
    test(l_r_rgbxi,  1024);
    test(l_g_rgbxi,  1024);
    return 0;
}