Add basic benchmark for tenvex

src/benchmarks/bench_main.cpp

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+#include <benchmark/benchmark.h>
+
+BENCHMARK_MAIN();

src/benchmarks/bench_vec4.cpp

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+#include "tenvex.h"
+
+#include <benchmark/benchmark.h>
+
+#include <vector>
+#include <random>
+#include <smmintrin.h>
+
+using namespace tnvx;
+
+// Runtime data so nothing folds to a compile-time constant.
+static std::vector<vec4> make_vecs(int n, unsigned seed)
+{
+    std::mt19937 rng(seed);
+    std::uniform_real_distribution<float> d(-1.0f, 1.0f);
+    std::vector<vec4> v;
+    v.reserve(n);
+    for (int i = 0; i < n; ++i)
+        v.push_back(vec4 { d(rng), d(rng), d(rng), 0.0f });
+    return v;
+}
+
+// =====================================================================
+// LATENCY: each iteration depends on the previous result (serial chain).
+// This is the metric for scattered everyday math: the result is needed
+// before moving on.
+// =====================================================================
+static void BM_Dot3_Latency(benchmark::State& state)
+{
+    vec4 a { 1.0f, 2.0f, 3.0f, 0.0f };
+    vec4 b { 0.5f, 0.5f, 0.5f, 0.0f };
+    float acc = 0.0f;
+    for (auto _ : state)
+    {
+        vec4 bb = b + vec4 { acc, 0.0f, 0.0f, 0.0f }; // depends on previous result
+        float d = dot3(a, bb);
+        acc = d * 1e-7f;                              // feedback = dependency chain
+        benchmark::DoNotOptimize(acc);
+    }
+}
+BENCHMARK(BM_Dot3_Latency);
+
+static void BM_Norm3_Latency(benchmark::State& state)
+{
+    vec4 v { 1.0f, 2.0f, 3.0f, 1.0f };
+    for (auto _ : state)
+    {
+        v = norm3(v) + vec4 { 1e-3f, 2e-3f, 3e-3f, 0.0f }; // chain through v
+        benchmark::DoNotOptimize(v);
+    }
+}
+BENCHMARK(BM_Norm3_Latency);
+
+// =====================================================================
+// THROUGHPUT: independent inputs, no cross-iteration dependency, so the
+// CPU can pipeline. Contrast to latency.
+// =====================================================================
+static void BM_Dot3_Throughput(benchmark::State& state)
+{
+    const auto a = make_vecs(1024, 1);
+    const auto b = make_vecs(1024, 2);
+    std::size_t i = 0;
+    for (auto _ : state)
+    {
+        float d = dot3(a[i], b[i]);
+        benchmark::DoNotOptimize(d);
+        i = (i + 1) & 1023;
+    }
+}
+BENCHMARK(BM_Dot3_Throughput);
+
+// =====================================================================
+// Compound expression: tenvex vs hand-written intrinsics.
+// If the numbers are roughly equal, the abstraction is zero-cost.
+// =====================================================================
+static void BM_Compound_tenvex(benchmark::State& state)
+{
+    const auto va = make_vecs(1024, 1);
+    const auto vb = make_vecs(1024, 2);
+    const auto vc = make_vecs(1024, 3);
+    std::size_t i = 0;
+    for (auto _ : state)
+    {
+        vec4 r = norm3(va[i] + vb[i] * 2.0f) * dot3(vb[i], vc[i]) + vc[i] * 3.0f;
+        benchmark::DoNotOptimize(r);
+        i = (i + 1) & 1023;
+    }
+}
+BENCHMARK(BM_Compound_tenvex);
+
+static __m128 dp3_raw(__m128 a, __m128 b) { return _mm_dp_ps(a, b, 0x7F); }
+
+static __m128 norm3_raw(__m128 v)
+{
+    __m128 len = _mm_sqrt_ps(dp3_raw(v, v));
+    return _mm_blend_ps(_mm_div_ps(v, len), v, 0b1000);
+}
+
+static void BM_Compound_intrinsics(benchmark::State& state)
+{
+    const auto va = make_vecs(1024, 1);
+    const auto vb = make_vecs(1024, 2);
+    const auto vc = make_vecs(1024, 3);
+    std::size_t i = 0;
+    for (auto _ : state)
+    {
+        __m128 a = va[i].eval(), b = vb[i].eval(), c = vc[i].eval();
+        __m128 t = norm3_raw(_mm_add_ps(a, _mm_mul_ps(b, _mm_set1_ps(2.0f))));
+        __m128 d = dp3_raw(b, c);
+        __m128 r = _mm_add_ps(_mm_mul_ps(t, d), _mm_mul_ps(c, _mm_set1_ps(3.0f)));
+        benchmark::DoNotOptimize(r);
+        i = (i + 1) & 1023;
+    }
+}
+BENCHMARK(BM_Compound_intrinsics);
+
+// =====================================================================
+// Gameplay-style query: do two units face roughly the same way?
+// Latency-bound - the answer is needed before branching on it.
+// =====================================================================
+static void BM_FacingSameWay(benchmark::State& state)
+{
+    vec4 fa = norm3(vec4 { 1.0f, 0.0f, 0.2f, 0.0f });
+    vec4 fb = vec4 { 0.9f, 0.1f, 0.1f, 0.0f };
+    float jitter = 0.0f;
+    for (auto _ : state)
+    {
+        vec4 f = norm3(fb + vec4 { jitter, 0.0f, 0.0f, 0.0f });
+        float c = dot3(fa, f);
+        bool same = c > 0.95f;
+        jitter = c * 1e-6f;
+        benchmark::DoNotOptimize(same);
+    }
+}
+BENCHMARK(BM_FacingSameWay);