reasampler/tests/test_tempo.cpp

// Standalone tests for reasampler::instrument::note::tempo — no VST3, no REAPER, no
// framework. Same fast assert loop as the sibling pure tests.
//
// Covers: BPM validation (the only rejection point, which is what makes the conversions
// total) including the tempos whose reciprocal is finite but whose conversions overflow;
// seconds-per-beat at several tempos; beats<->seconds and beats<->ms round-trips across
// tempos and signs; the proportionality between two tempos, asserted as a ratio rather than
// against any fixed seconds value.

#include "../src/core/instrument/note/tempo.h"

#include <cmath>
#include <cstdio>
#include <limits>

using namespace reasampler::instrument::note;

static int g_fail = 0;
#define CHECK(cond) do { if(!(cond)) { \
    std::printf("FAIL line %d: %s\n", __LINE__, #cond); ++g_fail; } } while(0)

static bool almostEqual(double a, double b, double eps = 1e-9) {
    return std::fabs(a - b) < eps;
}

static Tempo at(double bpm) {
    const std::optional<Tempo> t = Tempo::fromBpm(bpm);
    if (!t) { std::printf("FAIL: fixture tempo %f rejected\n", bpm); ++g_fail; }
    return t.value_or(Tempo::fromBpm(120.0).value());
}

// --- Validation ---------------------------------------------------------------

static void testUsableBpmIsAccepted() {
    const std::optional<Tempo> t = Tempo::fromBpm(137.5);
    CHECK(t.has_value());
    CHECK(t && almostEqual(t->bpm(), 137.5));
}

static void testUnusableBpmIsRejected() {
    CHECK(!Tempo::fromBpm(0.0).has_value());
    CHECK(!Tempo::fromBpm(-120.0).has_value());
    CHECK(!Tempo::fromBpm(std::numeric_limits<double>::quiet_NaN()).has_value());
    CHECK(!Tempo::fromBpm(std::numeric_limits<double>::infinity()).has_value());
    // Finite, positive, subnormal — but 60/bpm overflows to +inf, which turns
    // beatsToSeconds(0) into NaN downstream if let through.
    CHECK(!Tempo::fromBpm(1e-310).has_value());
}

static void testBpmWhoseReciprocalIsFineButWhoseConversionsOverflowIsRejected() {
    // The gap a guard on 60/bpm alone leaves open: the reciprocal is an ordinary finite
    // double, and the multiply that follows it is what blows up.
    CHECK(std::isfinite(60.0 / 1e-306));
    CHECK(!Tempo::fromBpm(1e-306).has_value());
    // The fast end fails in the other direction — the divide, not the multiply.
    CHECK(!Tempo::fromBpm(1e308).has_value());
}

static void testTheGuardAdmitsEveryRealTempoAndFarBeyond() {
    // The guard is structural, not musical, so it must not have narrowed onto the range of
    // tempos anyone would type. The extremes here are orders of magnitude past that.
    for (double bpm : {1e-200, 1e-6, 0.001, 1.0, 20.0, 120.0, 240.0, 960.0, 1e6, 1e100}) {
        CHECK(Tempo::fromBpm(bpm).has_value());
    }
}

static void testEveryAcceptedTempoConvertsTheWholeDomainFinitely() {
    // What the guard is FOR: past it, no conversion of a magnitude the module admits can
    // reach inf or NaN, in either unit or either direction.
    int accepted = 0, rejected = 0;
    for (double bpm : {1e-320, 1e-306, 1e-300, 1e-100, 1e-6, 0.5, 120.0, 1e6, 1e100, 1e250,
                       1e308}) {
        const std::optional<Tempo> t = Tempo::fromBpm(bpm);
        if (!t) { ++rejected; continue; }
        ++accepted;
        for (double m : {-kMaxConvertibleMagnitude, -1.0, 0.0, 1.0, kMaxConvertibleMagnitude}) {
            CHECK(std::isfinite(t->beatsToSeconds(m)));
            CHECK(std::isfinite(t->beatsToMs(m)));
            CHECK(std::isfinite(t->msToBeats(m)));
            CHECK(std::isfinite(t->secondsToBeats(msToSeconds(m))));
        }
    }
    // Neither half of the sweep may be empty, or the loop above proves nothing.
    CHECK(accepted > 0);
    CHECK(rejected > 0);
}

// --- Conversions ---------------------------------------------------------------

static void testSecondsPerBeatFollowsBpm() {
    CHECK(almostEqual(at(60.0).secondsPerBeat(), 1.0));
    CHECK(almostEqual(at(120.0).secondsPerBeat(), 0.5));
    CHECK(almostEqual(at(240.0).secondsPerBeat(), 0.25));
}

static void testBeatsToSecondsAtAKnownTempo() {
    // 90 BPM: one beat is 2/3 s, so four beats are 8/3 s.
    const Tempo t = at(90.0);
    CHECK(almostEqual(t.beatsToSeconds(1.0), 2.0 / 3.0));
    CHECK(almostEqual(t.beatsToSeconds(4.0), 8.0 / 3.0));
    CHECK(almostEqual(t.secondsToBeats(8.0 / 3.0), 4.0));
}

static void testBeatsToMsAtAKnownTempo() {
    // 150 BPM: one beat is 400 ms.
    const Tempo t = at(150.0);
    CHECK(almostEqual(t.beatsToMs(1.0), 400.0, 1e-6));
    CHECK(almostEqual(t.msToBeats(400.0), 1.0));
    CHECK(almostEqual(t.msToBeats(100.0), 0.25));
}

static void testMsAndBeatsRoundTripAcrossTemposAndSigns() {
    const double bpms[] = {33.0, 77.3, 120.0, 174.6, 300.0};
    const double values[] = {-500.0, -20.0, 0.0, 0.5, 250.0, 12345.678};
    for (double bpm : bpms) {
        const Tempo t = at(bpm);
        for (double ms : values) {
            CHECK(almostEqual(t.beatsToMs(t.msToBeats(ms)), ms, 1e-9 + 1e-9 * std::fabs(ms)));
        }
        for (double beats : values) {
            CHECK(almostEqual(t.msToBeats(t.beatsToMs(beats)), beats,
                              1e-9 + 1e-9 * std::fabs(beats)));
        }
    }
}

static void testSecondsRoundTrip() {
    const Tempo t = at(101.7);
    CHECK(almostEqual(t.secondsToBeats(t.beatsToSeconds(3.25)), 3.25));
    CHECK(almostEqual(t.beatsToSeconds(t.secondsToBeats(-1.75)), -1.75));
}

// --- Proportionality -----------------------------------------------------------

static void testHalvingTheTempoDoublesEveryBeatDuration() {
    // The ratio is the claim; no seconds value is asserted, so the test cannot encode a
    // fixed tempo of its own.
    const Tempo fast = at(140.0);
    const Tempo slow = at(70.0);
    for (double beats : {0.0625, 0.75, 2.0 / 3.0, 16.0, 256.0}) {
        CHECK(almostEqual(slow.beatsToSeconds(beats), 2.0 * fast.beatsToSeconds(beats), 1e-9));
    }
}

static void testSecondsScaleInverselyWithBpm() {
    const Tempo a = at(96.0);
    const Tempo b = at(123.0);
    const double beats = 3.5;
    CHECK(almostEqual(a.beatsToSeconds(beats) / b.beatsToSeconds(beats), 123.0 / 96.0));
}

static void testMillisecondsAreTempoFree() {
    // The ms<->seconds pair carries no tempo — that is what lets a ms-denominated offset
    // hold still while a beats-denominated one moves.
    CHECK(almostEqual(msToSeconds(250.0), 0.25));
    CHECK(almostEqual(secondsToMs(1.5), 1500.0));
    CHECK(almostEqual(msToSeconds(secondsToMs(0.037)), 0.037));
}

int main() {
    testUsableBpmIsAccepted();
    testUnusableBpmIsRejected();
    testBpmWhoseReciprocalIsFineButWhoseConversionsOverflowIsRejected();
    testTheGuardAdmitsEveryRealTempoAndFarBeyond();
    testEveryAcceptedTempoConvertsTheWholeDomainFinitely();

    testSecondsPerBeatFollowsBpm();
    testBeatsToSecondsAtAKnownTempo();
    testBeatsToMsAtAKnownTempo();
    testMsAndBeatsRoundTripAcrossTemposAndSigns();
    testSecondsRoundTrip();

    testHalvingTheTempoDoublesEveryBeatDuration();
    testSecondsScaleInverselyWithBpm();
    testMillisecondsAreTempoFree();

    if (g_fail == 0) std::printf("tempo: all tests passed\n");
    else std::printf("tempo: %d FAILED\n", g_fail);
    return g_fail == 0 ? 0 : 1;
}