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Sylpheed RE agent 679812f1c9 re: built-in 108 is deploy_squadron_ex — deploy plus a 1<<n selector ...

1146 sites in 22 stages, the second-largest unnamed built-in. Its method
sub_822646B8 (vtable slot 300) and built-in 2's sub_822642E0 (slot 12) are
190 and 199 instructions and differ in exactly one block. Diffed instruction
by instruction, 108 adds:

  lwz   r11, 16(r29)     the blob's slot-16 int
  cmpwi/blt/cmpwi/bgt    range-check n to [0, 31]
  slw   r21, r25, r11    r21 = 1 << n     <- a 32-bit selector
  ...                    default 1 when out of range

Everywhere built-in 2 passes its r21, 108 passes r20 and reserves r21 for the
mask, so the bit is an EXTRA argument to the same call rather than a
replacement. Both post the identical command word AB0100BA, opcode 256.

The operand is always a valid bit index: over all 1146 sites slot 16 is in
[0, 31], 1146 of 1146, none outside, so the out-of-range default never fires
in shipped content. Fifteen distinct values clustered at 16 (531x), 31
(165x), 20 (161x) and 2 (90x); 21 of 22 stages use more than one.

What the bit SELECTS is not established and the name does not claim it. There
is plainly a 32-bit space -- built-in 92 reportedly allocates a free bit by
OR-ing over live units, which would make 108 its "place in a named slot"
counterpart -- but I have not verified that, so the name says only what is
proven: the same deploy as built-in 2, with an extra selector.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

2026-08-26 01:31:39 +00:00

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