Changes in version 0.1.0 (2026-10-22)                  

First release.

  - Vendors Radford Neal's 'xsum' (stable version 3), patched so that no
    standard I/O reaches the compiled code; upstream's checker and
    fuzzer run against the vendored copy in CI.

  - A vignette, vignette("exact-summation"), explains why base sum()
    differs between platforms and how to sum in pieces and from C.

  - xsum() returns the exactly rounded sum of double, integer, logical
    and complex vectors, with na.rm, applying the same special-value
    rules on every platform. ALTREP vectors are read in blocks, never
    materialised.

  - zuexact_info() reports the vendored 'xsum' version, the accumulator
    threshold, SIMD and FMA support, and whether R has long doubles.

  - xsum_mean() divides the exact sum by the count with one rounding;
    xsum_weighted_mean() divides two exact sums.

  - xsum_dot(), xsum_sqnorm() and xsum_norm() include each product's
    rounding error (TwoProduct with fma()), so dot products are exactly
    rounded too.

  - xsum_cumsum() rounds every prefix sum exactly.

  - Accumulators as R values: xsum_acc(), xsum_add(), xsum_merge(),
    xsum_negate(), xsum_value() and xsum_mean_value() build exact sums
    in pieces, in any order, and across processes (they serialise).

  - xsum_rowsums(), xsum_colsums() and xsum_by() are exact versions of
    rowSums(), colSums() and rowsum(). Row sums work a block of rows at
    a time, so their extra memory does not grow with the number of rows.

  - A registered C interface, zuexact_api_v1 in inst/include/zuexact.h,
    gives other packages' C code the same exact accumulators, sums, dot
    products, merges and means, through LinkingTo: zuexact.

  - Every result is tested against exact rational arithmetic ('gmp'),
    PreciseSums::fsum(), the test262 Math.sumPrecise vectors and
    ill-conditioned inputs up to condition number 1e40, and must be
    bit-identical on every CI platform.