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takum32/64: record libtakum C-reference parity witness (Variant B) - #1335
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Cross-check merged curated packs (#1327/#1328) against independent libtakum ISO C99 reference (Hunhold, ISC), built in-sandbox and called via ctypes. takum32 parity DONE: encode bit-for-bit 15/15; decode-law parity on 2,000,000 codes (max rel err 7.5e-15 long-double noise, 0 law breaks); our mpmath oracle is the correctly-rounded one (0 ULP vs 400-bit) where libtakum powl diverges (<=65 ULP at extreme exponents). C reference confirms decode law + 15 codes. takum64 parity PARTIAL (honest): decode-VALUE parity at f64 on all 15 (correctly-rounded, <=1 ULP vs libtakum); ENCODE bit-pattern parity NOT claimed -- curated mantissa=0 grid anchor vs round-to-nearest code both decode to same f64; 59-bit takum64 mantissa makes them distinct (takum32 coincides). Witness-only: witnesses[] + format_notes + INDEX sha256 + NOW.md. No vector data, no counts, no SSOT, no gen/ edits. SW stays 72/83. WP-18 gate CLEAN. [verified SW]; NOT [exhaustive]; NOT a silicon/HW claim.
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Summary
Cross-check the merged curated takum32/takum64 bitexact packs (#1327/#1328) against the independent libtakum ISO C99 reference (Laslo Hunhold, ISC license) — built in-sandbox from
src/{conversion,codec,util}.cand called via ctypes as an independent 2nd decoder/encoder (takum_log32/64_from/to_float64).Findings
takum32 — parity DONE (strong):
takum_log32_from_float64(input_f64)== our stored bits on 15/15 curated vectors.powl(sqrt(e), l)carries the transcendental rounding. The C reference confirms the decode law and the 15 curated codes.takum64 — parity PARTIAL (honest limitation):
decoded_f64equal the correctly-rounded f64 of the true takum decode (mpmath 1200-bit); libtakum decodes the same codes to the same f64 (≤1 ULP).Change scope
libtakum_c_paritywitness entry in both packs (NOT DONE → DONE/PARTIAL with results).format_notesin each pack.sha256inINDEX_all_formats.json.docs/NOW.mdsection added (now-sync-gate).gen/changes. SW-axis stays 72/83. WP-18 conformance-integrity-gate (A/B/C/D/D2/E) CLEAN locally.[verified SW]cross-check; NOT[exhaustive]on 2^32/2^64; NOT a silicon/HW claim.Closes #1334.