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perf: compare variable and attribute names in place - #78
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NOVARY dimensions aren't physically stored, so counting them read past each variable's data. r-variables already dropped them; z-variables now share that path. Matches CDFpp and cdflib.
Lookups by name scanned each record's name field for its terminator and compared a view element-wise; attribute lookup also parsed every ADR first. Compare with one memcmp in the buffer instead, and read an ADR's name only when it is returned. Name fields are 64 bytes in CDF v2, not 256, so a v2 name filling its field was read into the following bytes.
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Stacked on #77.
Name lookups (
ds[name],haskey,var.attrib[name],attrib(ds, name)) scanned each record's name field for its terminator and compared a view element-wise; attribute lookup also parsed every ADR first. Now onememcmpin the buffer, checking the terminator right after the requested length.ADRkeeps the name's position instead of reading it, so the name is read only when returned (adr_name). First-call time is unchanged: 175–177 ms for openingac_h0_mfiand reading every variable's attributes, before and after.Looking up every variable / every variable attribute, before → after:
ds[k]all varsv.attrib[a]allAlso: name fields are 64 bytes in CDF v2 (cdflib, CDFpp
cdf_string_field_t<version_t, 256, 64>), not 256, soreadnameread a v2 name filling its field into the following bytes. It only shows on v2 r-variables with dimensions, where DimVarys (-1) follows the name; no fixture has one.Full suite passes, including JET and trim.