mirror of
https://github.com/irmen/prog8.git
synced 2024-11-22 15:33:02 +00:00
90 lines
3.2 KiB
Lua
90 lines
3.2 KiB
Lua
adpcm {
|
|
|
|
sub decode_benchmark(uword max_time) -> uword {
|
|
uword num_blocks
|
|
txt.nl()
|
|
cbm.SETTIM(0,0,0)
|
|
|
|
while cbm.RDTIM16()<max_time {
|
|
adpcm.init(0,0)
|
|
uword @requirezp nibbles_ptr = $a000 ; for benchmark purposes, the exact nibbles don't really matter, so we just take the basic ROM as input
|
|
repeat 252/2 {
|
|
unroll 2 {
|
|
ubyte @zp nibble = @(nibbles_ptr)
|
|
adpcm.decode_nibble(nibble & 15) ; first word (note: upper nibble needs to be zero!)
|
|
adpcm.decode_nibble(nibble>>4) ; second word (note: upper nibble is zero, after the shifts.)
|
|
nibbles_ptr++
|
|
}
|
|
}
|
|
num_blocks++
|
|
txt.chrout('.')
|
|
}
|
|
|
|
return num_blocks
|
|
}
|
|
|
|
; IMA ADPCM decoder. Supports mono and stereo streams.
|
|
|
|
ubyte[] t_index = [ -1, -1, -1, -1, 2, 4, 6, 8, -1, -1, -1, -1, 2, 4, 6, 8]
|
|
uword[] @split t_step = [
|
|
7, 8, 9, 10, 11, 12, 13, 14,
|
|
16, 17, 19, 21, 23, 25, 28, 31,
|
|
34, 37, 41, 45, 50, 55, 60, 66,
|
|
73, 80, 88, 97, 107, 118, 130, 143,
|
|
157, 173, 190, 209, 230, 253, 279, 307,
|
|
337, 371, 408, 449, 494, 544, 598, 658,
|
|
724, 796, 876, 963, 1060, 1166, 1282, 1411,
|
|
1552, 1707, 1878, 2066, 2272, 2499, 2749, 3024,
|
|
3327, 3660, 4026, 4428, 4871, 5358, 5894, 6484,
|
|
7132, 7845, 8630, 9493, 10442, 11487, 12635, 13899,
|
|
15289, 16818, 18500, 20350, 22385, 24623, 27086, 29794,
|
|
32767]
|
|
|
|
uword @requirezp predict ; decoded 16 bit pcm sample for first channel.
|
|
ubyte @requirezp index
|
|
uword @requirezp pstep
|
|
|
|
sub init(uword startPredict, ubyte startIndex) {
|
|
; initialize first decoding channel.
|
|
predict = startPredict
|
|
index = startIndex
|
|
pstep = t_step[index]
|
|
}
|
|
|
|
sub decode_nibble(ubyte @zp nibble) {
|
|
; Decoder for a single nibble for the first channel. (value of 'nibble' needs to be strictly 0-15 !)
|
|
; This is the hotspot of the decoder algorithm!
|
|
; Note that the generated assembly from this is pretty efficient,
|
|
; rewriting it by hand in asm seems to improve it only ~10%.
|
|
cx16.r0s = 0 ; difference
|
|
if nibble & %0100 !=0
|
|
cx16.r0s += pstep
|
|
pstep >>= 1
|
|
if nibble & %0010 !=0
|
|
cx16.r0s += pstep
|
|
pstep >>= 1
|
|
if nibble & %0001 !=0
|
|
cx16.r0s += pstep
|
|
pstep >>= 1
|
|
cx16.r0s += pstep
|
|
if nibble & %1000 !=0
|
|
predict -= cx16.r0
|
|
else
|
|
predict += cx16.r0
|
|
|
|
; NOTE: the original C/Python code uses a 32 bits prediction value and clips it to a 16 bit word
|
|
; but for speed reasons we only work with 16 bit words here all the time (with possible clipping error)
|
|
; if predicted > 32767:
|
|
; predicted = 32767
|
|
; elif predicted < -32767:
|
|
; predicted = - 32767
|
|
|
|
index += t_index[nibble]
|
|
if_neg
|
|
index = 0
|
|
else if index >= len(t_step)-1
|
|
index = len(t_step)-1
|
|
pstep = t_step[index]
|
|
}
|
|
}
|