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696d10f1bb
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1) Reduce the number of iterations in the Horner scheme for operands with
a negative adjusted exponent. Previously the number was overestimated
quite generously.
2) The function _mpd_get_exp_iterations() now has an ACL2 proof and
is rewritten accordingly.
3) The proof relies on abs(op) > 9 * 10**(-prec-1), so operands without
that property are now handled by the new function _mpd_qexp_check_one().
4) The error analysis for the evaluation of the truncated Taylor series
in Hull&Abrham's paper relies on the fact that the reduced operand
'r' has fewer than context.prec digits.
Since the operands may have more than context.prec digits, a new ACL2
proof covers the case that r.digits > context.prec. To facilitate the
proof, the Horner step now uses fma instead of rounding twice in
multiply/add.
Changes in mpd_qexp():
----------------------
1) Fix a bound in the correct rounding loop that was too optimistic. In
practice results were always correctly rounded, because it is unlikely
that the error in _mpd_qexp() ever reaches the theoretical maximum.
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| .. | ||
| libmpdec | ||
| tests | ||
| _decimal.c | ||
| docstrings.h | ||
| ISSUES.txt | ||
| README.txt | ||
About ===== _decimal.c is a wrapper for the libmpdec library. libmpdec is a fast C library for correctly-rounded arbitrary precision decimal floating point arithmetic. It is a complete implementation of Mike Cowlishaw/IBM's General Decimal Arithmetic Specification. Build process for the module ============================ As usual, the build process for _decimal.so is driven by setup.py in the top level directory. setup.py autodetects the following build configurations: 1) x64 - 64-bit Python, x86_64 processor (AMD, Intel) 2) uint128 - 64-bit Python, compiler provides __uint128_t (gcc) 3) ansi64 - 64-bit Python, ANSI C 4) ppro - 32-bit Python, x86 CPU, PentiumPro or later 5) ansi32 - 32-bit Python, ANSI C 6) ansi-legacy - 32-bit Python, compiler without uint64_t 7) universal - Mac OS only (multi-arch) It is possible to override autodetection by exporting: PYTHON_DECIMAL_WITH_MACHINE=value, where value is one of the above options. NOTE ==== decimal.so is not built from a static libmpdec.a since doing so led to failures on AIX (user report) and Windows (mixing static and dynamic CRTs causes locale problems and more).