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feat(efloat): implement core multiplication/division engines and standard regression tests (#1103)
* feat(efloat): implement core multiplication/division engines and standard regression tests (#1090) Implement constexpr-compatible static multiply_limbs (reversing inputs for LSB-first long multiplication, then reversing the product back) and static divide_limbs (bit-by-bit restoring division) to support MSB-first limb layouts. Implement constexpr operator*=, operator/=, and their scalar double equivalents in efloat_impl.hpp, handling all special cases (NaN, Inf, Zero math rules), exponent math, and precision limits. Refactor all underlying limb helpers (shift_right, grow_for_shift, align_sizes, add_limbs, subtract_limbs, and normalize) to cleanly and consistently use the native MSB-first layout, which simplifies trailing-zero truncation to pop_back() and resolves all historical fuzzer offsets. Add comprehensive standard-conforming regression tests for multiplication.cpp and division.cpp, testing algebraic invariants, special values, and fuzzing strict invariants (commutativity, identity, self-division, zero-product). Resolves #1090 Relates to Epic #1101 * fix(efloat): resolve compile-time constexpr.cpp failures and multiplication typos Correct the static assertion inside constexpr.cpp to expect isnan() for constexpr division on 0/0, which matches our correct mathematical implementation. Correct the expected product value of 123456 * 654321 inside multiplication.cpp to the true exact product 80779853376.0, resolving the limb expansion test failure. Relates to #1090, #1103
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Lines changed: 594 additions & 31 deletions

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‎elastic/efloat/api/constexpr.cpp‎

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@@ -178,7 +178,7 @@ try {
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x /= y;
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return x;
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}();
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static_assert(div_eq.iszero(), "constexpr /= stub leaves zero unchanged");
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static_assert(div_eq.isnan(), "constexpr /= on 0/0 produces NaN");
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}
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// ----------------------------------------------------------------------------

‎elastic/efloat/arithmetic/division.cpp‎

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// division.cpp: regression tests for efloat division.
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//
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// REGRESSION_LEVEL convention (intensity progression):
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// LEVEL 1 -- all foundational hand-curated tests: algebraic invariants,
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// hostile arithmetic corner cases (round-to-even, massive
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// exponent gaps, complete overlap), subnormal boundaries,
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// IEEE 754 special values.
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// LEVEL 2 -- property-based fuzzer over random multi-component expansions
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// (~1,000 iterations per invariant).
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// LEVEL 3 -- same fuzzer at higher intensity (~100,000 iterations).
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// LEVEL 4 -- exhaustive fuzzer (~10,000,000 iterations).
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//
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// Copyright (C) 2017 Stillwater Supercomputing, Inc.
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// SPDX-License-Identifier: MIT
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//
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// This file is part of the universal numbers project, which is released under an MIT Open Source license.
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#include <universal/utility/directives.hpp>
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#include <cmath>
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#include <limits>
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#include <random>
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#include <universal/number/efloat/efloat.hpp>
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#include <universal/verification/test_suite.hpp>
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#include <universal/verification/efloat_test_support.hpp>
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namespace {
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// =========================================================================
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// LEVEL 1: foundational hand-curated tests
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// =========================================================================
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int VerifyEfloatDivision(bool reportTestCases) {
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using namespace sw::universal;
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int nrOfFailedTestCases = 0;
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// --- Algebraic invariants ---
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// Identity: a / 1.0 == a
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if (reportTestCases) std::cout << " Identity...\n";
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{
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efloat<16> a(1.234567e+15);
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efloat<16> one(1.0);
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efloat<16> result = a / one;
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if (result != a) {
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if (reportTestCases) std::cout << " FAIL a / 1 != a\n";
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++nrOfFailedTestCases;
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}
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}
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// Self divisor: a / a == 1.0
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if (reportTestCases) std::cout << " Self divisor...\n";
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{
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efloat<16> a(1.234567e+15);
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efloat<16> result = a / a;
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efloat<16> expected(1.0);
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if (result != expected) {
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if (reportTestCases) std::cout << " FAIL a / a != 1\n";
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++nrOfFailedTestCases;
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}
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}
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// Zero dividend: 0.0 / a == 0.0
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if (reportTestCases) std::cout << " Zero dividend...\n";
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{
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efloat<16> a(1.234567e+15);
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efloat<16> zero(0.0);
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efloat<16> result = zero / a;
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if (!result.iszero()) {
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if (reportTestCases) std::cout << " FAIL 0 / a != 0\n";
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++nrOfFailedTestCases;
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}
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}
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// --- Hostile arithmetic ---
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// Exact division: 2^40 / 2^20 = 2^20
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if (reportTestCases) std::cout << " Limb contraction (exact powers of 2)...\n";
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{
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efloat<16> a(1099511627776.0); // 2^40
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efloat<16> b(1048576.0); // 2^20
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efloat<16> result = a / b;
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efloat<16> expected(1048576.0); // 2^20
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if (result != expected) {
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if (reportTestCases) {
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std::cout << " FAIL limb contraction value mismatch. Result: " << result << " Expected: " << expected << "\n";
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}
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++nrOfFailedTestCases;
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}
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}
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// --- IEEE 754 special values ---
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double qnan = std::numeric_limits<double>::quiet_NaN();
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double pinf = std::numeric_limits<double>::infinity();
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double ninf = -pinf;
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if (reportTestCases) std::cout << " NaN / finite...\n";
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{
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efloat<16> a(1.0), n(qnan);
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if (!(n / a).isnan()) { if (reportTestCases) std::cout << " FAIL\n"; ++nrOfFailedTestCases; }
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}
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if (reportTestCases) std::cout << " finite / +Inf...\n";
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{
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efloat<16> a(1.0), inf(pinf);
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if (!(a / inf).iszero()) { if (reportTestCases) std::cout << " FAIL\n"; ++nrOfFailedTestCases; }
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}
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if (reportTestCases) std::cout << " finite / Zero (Divide by Zero)...\n";
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{
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efloat<16> a(1.0), zero(0.0);
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if (!(a / zero).isinf()) { if (reportTestCases) std::cout << " FAIL\n"; ++nrOfFailedTestCases; }
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}
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if (reportTestCases) std::cout << " Zero / Zero...\n";
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{
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efloat<16> zero1(0.0), zero2(0.0);
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if (!(zero1 / zero2).isnan()) { if (reportTestCases) std::cout << " FAIL\n"; ++nrOfFailedTestCases; }
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}
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return nrOfFailedTestCases;
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}
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// =========================================================================
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// Fuzzer infrastructure
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// =========================================================================
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int VerifyEfloatDivision_Fuzz(bool reportTestCases, unsigned nrIterations) {
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using namespace sw::universal;
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const uint64_t seed = 0xC0FFEE'A11CEULL;
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std::mt19937_64 rng(seed);
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int nrOfFailedTestCases = 0;
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efloat<16> one(1.0);
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efloat<16> zero(0.0);
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for (unsigned i = 0; i < nrIterations; ++i) {
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efloat<16> a = random_efloat<16>(rng);
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// Identity: a / 1 == a
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if (a / one != a) {
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if (reportTestCases) std::cout << " FAIL identity (seed=0x" << std::hex << seed << " iter=" << std::dec << i << ")\n";
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++nrOfFailedTestCases;
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}
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// Self divisor: a / a == 1
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if (a / a != one) {
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if (reportTestCases) std::cout << " FAIL self divisor (seed=0x" << std::hex << seed << " iter=" << std::dec << i << ")\n";
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++nrOfFailedTestCases;
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}
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// Zero: 0 / a == 0
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if (zero / a != zero) {
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if (reportTestCases) std::cout << " FAIL zero (seed=0x" << std::hex << seed << " iter=" << std::dec << i << ")\n";
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++nrOfFailedTestCases;
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}
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}
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return nrOfFailedTestCases;
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}
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} // anonymous namespace
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// Regression testing guards
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#define MANUAL_TESTING 0
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#ifndef REGRESSION_LEVEL_OVERRIDE
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# undef REGRESSION_LEVEL_1
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# undef REGRESSION_LEVEL_2
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# undef REGRESSION_LEVEL_3
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# undef REGRESSION_LEVEL_4
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# define REGRESSION_LEVEL_1 1
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# define REGRESSION_LEVEL_2 0
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# define REGRESSION_LEVEL_3 0
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# define REGRESSION_LEVEL_4 0
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#endif
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int main() try {
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using namespace sw::universal;
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std::string test_suite = "efloat division";
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std::string test_tag = "division";
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bool reportTestCases = true;
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int nrOfFailedTestCases = 0;
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ReportTestSuiteHeader(test_suite, reportTestCases);
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#if MANUAL_TESTING
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision(reportTestCases), "efloat", "division manual");
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ReportTestSuiteResults(test_suite, nrOfFailedTestCases);
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return EXIT_SUCCESS; // ignore errors in manual mode
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#else
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# if REGRESSION_LEVEL_1
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision(reportTestCases), "efloat", "division foundational");
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision_Fuzz(reportTestCases, 100), "efloat", "division fuzz x100");
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# endif
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# if REGRESSION_LEVEL_2
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision_Fuzz(reportTestCases, 1000), "efloat", "division fuzz x1k");
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# endif
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# if REGRESSION_LEVEL_3
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision_Fuzz(reportTestCases, 10000), "efloat", "division fuzz x10k");
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# endif
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# if REGRESSION_LEVEL_4
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nrOfFailedTestCases += ReportTestResult(VerifyEfloatDivision_Fuzz(reportTestCases, 100000), "efloat", "division fuzz x100k");
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# endif
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ReportTestSuiteResults(test_suite, nrOfFailedTestCases);
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return (nrOfFailedTestCases > 0 ? EXIT_FAILURE : EXIT_SUCCESS);
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#endif // MANUAL_TESTING
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}
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catch (const std::exception& e) {
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std::cerr << "Caught exception: " << e.what() << std::endl;
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return EXIT_FAILURE;
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}
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catch (...) {
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std::cerr << "Caught unknown exception" << std::endl;
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return EXIT_FAILURE;
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}

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