[FFmpeg-devel] [PATCH] dsicinav: reduce cinaudio_delta16_table

[Reimar Döffinger]

On Wed, Jul 02, 2008 at 07:12:03PM +0200, Gregory Montoir wrote:
> Index: libavcodec/dsicinav.c
> ===================================================================
> --- libavcodec/dsicinav.c	(r?vision 14047)
> +++ libavcodec/dsicinav.c	(copie de travail)
> @@ -50,23 +50,7 @@
> 
> 
>  /* table defining a geometric sequence with multiplier = 32767 ^ (1 / 128) */
> -static const int16_t cinaudio_delta16_table[256] = {
> -         0,      0,      0,      0,      0,      0,      0,      0,
> -         0,      0,      0,      0,      0,      0,      0,      0,
> -         0,      0,      0, -30210, -27853, -25680, -23677, -21829,
> -    -20126, -18556, -17108, -15774, -14543, -13408, -12362, -11398,
> -    -10508,  -9689,  -8933,  -8236,  -7593,  -7001,  -6455,  -5951,
> -     -5487,  -5059,  -4664,  -4300,  -3964,  -3655,  -3370,  -3107,
> -     -2865,  -2641,  -2435,  -2245,  -2070,  -1908,  -1759,  -1622,
> -     -1495,  -1379,  -1271,  -1172,  -1080,   -996,   -918,   -847,
> -      -781,   -720,   -663,   -612,   -564,   -520,   -479,   -442,
> -      -407,   -376,   -346,   -319,   -294,   -271,   -250,   -230,
> -      -212,   -196,   -181,   -166,   -153,   -141,   -130,   -120,
> -      -111,   -102,    -94,    -87,    -80,    -74,    -68,    -62,
> -       -58,    -53,    -49,    -45,    -41,    -38,    -35,    -32,
> -       -30,    -27,    -25,    -23,    -21,    -20,    -18,    -17,
> -       -15,    -14,    -13,    -12,    -11,    -10,     -9,     -8,
> -        -7,     -6,     -5,     -4,     -3,     -2,     -1,      0,
> +static const int16_t cinaudio_delta16_table[128] = {
>           0,      1,      2,      3,      4,      5,      6,      7,
>           8,      9,     10,     11,     12,     13,     14,     15,
>          17,     18,     20,     21,     23,     25,     27,     30,
> @@ -326,7 +310,11 @@
>          buf_size -= 2;
>      }
>      while (buf_size > 0) {
> -        cin->delta += cinaudio_delta16_table[*src++];
> +        if (*src & 0x80)
> +            cin->delta += cinaudio_delta16_table[*src - 128];
> +        else
> +            cin->delta -= cinaudio_delta16_table[127 - *src];
> +        src++;

Well, it would be slightly simpler to keep the first part of the table
and do

> +        if (*src & 0x80)
> +            cin->delta -= cinaudio_delta16_table[255 - *src];
> +        else
> +            cin->delta += cinaudio_delta16_table[*src];