Download Play: Difference between revisions
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The checksum stored in the above data frame header is then calculated using this checksum seed. | The checksum stored in the above data frame header is then calculated using this checksum seed. | ||
First, the calc_checksum is initialized to 0. Then calc_checksum is added with ''all'' words in the data frame loaded as big-endian, with the data-frame checksum cleared to zero here. If the frame_size isn't word-aligned, the remaining <4-bytes are loaded as big-endian for adding as well. | |||
Then this is run: | |||
//During init before the above adding, shift and count are initialized: | |||
//shift = (((u8*)&checksum_seed)[2] & 0xf) + 0x4; | |||
//count = (((u8*)&checksum_seed)[3] & 0x7) + 0x2; | |||
for(pos=0; pos<count; pos++)checksum = (checksum<<shift | checksum>>shift) ^ checksum_seed;//The u32 checksum_seed is byte-swapped on 3DS for this. | |||
Lastly the calculated checksum is written to output as big-endian(hence on 3DS it's byte-swapped before writing to output). | |||
==== Frames ==== | ==== Frames ==== | ||