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Dropped the q-bit (previous-perturb) from cksum tags

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Now that we perturb commit cksums with the odd-parity zero, the q-bit no
longer serves a purpose other than extra debug info. But this is a
double-edged sword, because redundant info just means another thing that
can go wrong.

For example, should we assert? If the q-bit doesn't reflect the
previous-perturb state it's a bug, but the only thing that would break
would be the q-bit itself. And if we don't assert what's the point of
keeping the q-bit around?

Dropping the q-bit avoids answering this question and saves a bit of
code:

           code          stack          ctx
  before: 37772           2608          620
  after:  37768 (-0.0%)   2608 (+0.0%)  620 (+0.0%)
This commit is contained in:
Christopher Haster
2025-01-10 15:55:48 -06:00
parent d08d254cd2
commit b6ab323eb1
7 changed files with 22 additions and 45 deletions
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10
scripts/dbgmtree.py
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@@ -48,9 +48,8 @@ TAG_B = 0x0000
TAG_R = 0x2000
TAG_LE = 0x0000
TAG_GT = 0x1000
TAG_CKSUM = 0x3000 ## 0x3c0p v-11 cccc ---- --qp
TAG_CKSUM = 0x3000 ## 0x3c0p v-11 cccc ---- ---p
TAG_P = 0x0001
TAG_Q = 0x0002
TAG_NOTE = 0x3100 # 0x3100 v-11 ---1 ---- ----
TAG_ECKSUM = 0x3200 # 0x3200 v-11 --1- ---- ----
@@ -254,10 +253,9 @@ def tagrepr(tag, w=None, size=None, off=None):
else ' -%d' % size if size
else '')
elif (tag & 0x7f00) == TAG_CKSUM:
return 'cksum%s%s%s%s%s' % (
'q' if not tag & 0xfc and tag & TAG_Q else '',
'p' if not tag & 0xfc and tag & TAG_P else '',
' 0x%02x' % (tag & 0xff) if tag & 0xfc else '',
return 'cksum%s%s%s%s' % (
'p' if not tag & 0xfe and tag & TAG_P else '',
' 0x%02x' % (tag & 0xff) if tag & 0xfe else '',
' w%d' % w if w else '',
' %s' % size if size is not None else '')
elif (tag & 0x7f00) == TAG_NOTE: