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Save_GIF() translated and clarified comments.

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No change in algorithm, same output.
This commit is contained in:
Thomas Bernard 2018-01-03 23:53:11 +01:00
parent 9f3af34968
commit 8c6f89af46
1 changed files with 30 additions and 26 deletions
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56
src/fileformats.c
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@ -3312,7 +3312,8 @@ void Save_GIF(T_IO_Context * context)
GIF_remainder_bits=0; GIF_remainder_bits=0;
GIF_remainder_byte=0; GIF_remainder_byte=0;
index=4096; #define GIF_INVALID_CODE (65535)
index=GIF_INVALID_CODE;
File_error=0; File_error=0;
GIF_stop=0; GIF_stop=0;
@ -3323,8 +3324,8 @@ void Save_GIF(T_IO_Context * context)
GIF_set_code(clear); //256 for 8bpp GIF_set_code(clear); //256 for 8bpp
for (start=0;start<4096;start++) for (start=0;start<4096;start++)
{ {
alphabet_daughter[start]=4096; alphabet_daughter[start] = GIF_INVALID_CODE;
alphabet_sister[start]=4096; alphabet_sister[start] = GIF_INVALID_CODE;
} }
////////////////////////////////////////////// COMPRESSION LZW // ////////////////////////////////////////////// COMPRESSION LZW //
@ -3336,10 +3337,8 @@ void Save_GIF(T_IO_Context * context)
{ {
current_char=GIF_next_pixel(context, &IDB); current_char=GIF_next_pixel(context, &IDB);
// On regarde si dans la table on aurait pas une chaîne // look for (current_string,current_char) in the alphabet
// équivalente à current_string+Caractere while ( (index != GIF_INVALID_CODE) &&
while ( (index<alphabet_free) &&
( (current_string!=alphabet_prefix[index]) || ( (current_string!=alphabet_prefix[index]) ||
(current_char !=alphabet_suffix[index]) ) ) (current_char !=alphabet_suffix[index]) ) )
{ {
@ -3348,10 +3347,11 @@ void Save_GIF(T_IO_Context * context)
index=alphabet_sister[index]; index=alphabet_sister[index];
} }
if (index<alphabet_free) if (index != GIF_INVALID_CODE)
{ {
// On sait ici que la current_string+Caractere se trouve // (current_string,current_char) == (alphabet_prefix,alphabet_suffix)[index]
// en position index dans les tables. // We have found (current_string,current_char) in the alphabet
// at the index position. So go on and prepare for then next character
descend=1; descend=1;
start=current_string=index; start=current_string=index;
@ -3359,30 +3359,34 @@ void Save_GIF(T_IO_Context * context)
} }
else else
{ {
// On fait la jonction entre la current_string et l'actuelle // (current_string,current_char) was not found in the alphabet
if (descend) // so write current_string to the Gif stream
alphabet_daughter[start]=alphabet_free;
else
alphabet_sister[start]=alphabet_free;
// On rajoute la chaîne current_string+Caractere à la table
alphabet_prefix[alphabet_free ]=current_string;
alphabet_suffix[alphabet_free++]=current_char;
// On écrit le code dans le fichier
GIF_set_code(current_string); GIF_set_code(current_string);
if(alphabet_free < 4096) {
// link current_string and the new one
if (descend)
alphabet_daughter[start]=alphabet_free;
else
alphabet_sister[start]=alphabet_free;
// add (current_string,current_char) to the alphabet
alphabet_prefix[alphabet_free]=current_string;
alphabet_suffix[alphabet_free]=current_char;
alphabet_free++;
}
if (alphabet_free>0xFFF) if (alphabet_free >= 4096)
{ {
// Réintialisation de la table: // clear alphabet
GIF_set_code(clear); // 256 for 8bpp GIF_set_code(clear); // 256 for 8bpp
alphabet_free=clear+2; // 258 for 8bpp alphabet_free=clear+2; // 258 for 8bpp
GIF_nb_bits =IDB.Nb_bits_pixel + 1; // 9 for 8bpp GIF_nb_bits =IDB.Nb_bits_pixel + 1; // 9 for 8bpp
alphabet_max =clear+clear-1; // 511 for 8bpp alphabet_max =clear+clear-1; // 511 for 8bpp
for (start=0;start<4096;start++) for (start=0;start<4096;start++)
{ {
alphabet_daughter[start]=4096; alphabet_daughter[start] = GIF_INVALID_CODE;
alphabet_sister[start]=4096; alphabet_sister[start] = GIF_INVALID_CODE;
} }
} }
else if (alphabet_free>alphabet_max+1) else if (alphabet_free>alphabet_max+1)
@ -3393,7 +3397,7 @@ void Save_GIF(T_IO_Context * context)
alphabet_max=(1<<GIF_nb_bits)-1; alphabet_max=(1<<GIF_nb_bits)-1;
} }
// On initialise la current_string et le reste pour la suite // initialize current_string as the string "current_char"
index=alphabet_daughter[current_char]; index=alphabet_daughter[current_char];
start=current_string=current_char; start=current_string=current_char;
descend=1; descend=1;