Adopted mask bits for tag lookup/append

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This lets us cram in one more mask for potential redund bits:

  name                 tag    mask
  LFSR_TAG_MASK0    0x0000  0x0fff  ---- 1111 1111 1111
  LFSR_TAG_MASK2    0x1000  0x0ffc  ---- 1111 1111 11--
  LFSR_TAG_MASK8    0x2000  0x0f00  ---- 1111 ---- ----
  LFSR_TAG_MASK12   0x3000  0x0000  ---- ---- ---- ----
                                    '.-' '.-' '---.---'
                          mode bits -'    |       |   ^
                            suptype ------'       |   |
                            subtype --------------'   |
                        redund bits ------------------'

I toyed around with a bitwise alternative to the lookup table, but
couldn't come up with anything simpler than these:

- 0xfff & ~((((1<<((i>>1)*8))-1) << ((i&1)*4)) | ((1<<(i*2))-1))
- 0xfff & ~((1 << (((i>>1)*8)+((i&1)<<(1+(i>>1)))))-1)
- 0xfff & ~((1<<(2*i*i))-1) (requires multiply and 32-bit shift)

---

This also replaces the mdir/rbyd/btree/mtree lookup/sublookup/suplookup
functions with a single flexible lookup function that accepts tag masks.

This ended up adding a bit of code/stack (the extra NULL args are
surprisingly pricey), but will hopefully make the redund bits
easier/cheaper to use:

           code          stack          ctx
  before: 35548           2472          636
  after:  35584 (+0.1%)   2480 (+0.3%)  636 (+0.0%)

...

This commit is contained in:

Christopher Haster

2025-04-18 02:51:03 -05:00

parent 8f1ccf089e

commit 200830aafe

6 changed files with 1451 additions and 1502 deletions

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tests/test_mtree.toml

+201 -201

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