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minjaesong
2026-04-29 15:41:47 +09:00
parent 176766b793
commit 737b1cebe7
1 changed files with 15 additions and 22 deletions
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37
it2taud.py
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@@ -302,40 +302,33 @@ def _it214_decompress_block(payload: bytes, num_samples: int,
v = read_bits(width)
if width <= 6:
# Short form: top bit == escape trigger
# Short form: top bit == escape trigger; read escape_bits for new width.
# Reference: cubic.org/itsex.c (Jeffrey Lim, IT author) — no skip-self.
if v == (1 << (width - 1)):
new_w = read_bits(escape_bits) + 1
if new_w >= width:
new_w += 1
width = new_w
width = read_bits(escape_bits) + 1
continue
elif width < init_width:
# Mid form: escape codes are in the top half of the unsigned range.
# border = (2^(width-1)) - range_count (= (0x100 >> (9-width)) - 8 per reference).
# Escape if v > border; new width = v - border (adjusted for skip-over-self).
border = (1 << (width - 1)) - range_count
# Mid form. border = (all-ones mask) >> (init_width - width).
# For 8-bit: 0xFF>>(9-w) → 63 (w=7), 127 (w=8).
# Escape when v > border; new width = v - border directly, no skip-self.
# Reference: cubic.org/itsex.c, OpenMPT ITTools.cpp.
mask = (1 << (init_width - 1)) - 1 # 0xFF (8-bit) or 0xFFFF (16-bit)
border = mask >> (init_width - width)
if v > border:
new_w = v - border # 1..range_count
if new_w >= width:
new_w += 1
width = new_w
width = v - border
continue
else:
# Full form: top bit (bit init_width-1) is escape flag
# Full form: top bit (bit init_width-1) is escape flag.
# new width = lower bits + 1, no skip-self.
top_bit = 1 << (init_width - 1)
if v & top_bit:
new_w = (v & (top_bit - 1)) + 1
if new_w >= width:
new_w += 1
width = new_w
width = (v & (top_bit - 1)) + 1
continue
# Real sample: sign-extend delta and accumulate.
# Full-form (width == init_width): top bit was the escape flag, so the
# actual signed delta occupies the lower (init_width-1) bits — equivalent
# to C's (int8)val / (int16)val. All other widths use their full width.
# Real sample delta. For full-form the top bit was the escape flag so the
# signed delta is in the lower (init_width-1) bits — same as C's (int8)value.
delta = _sign_extend(v, min(width, init_width - 1))
if is_16bit:
d1 = _wrap16(d1 + delta)