2026-01-27T15:19:25

integrate.c

@@ -0,0 +1,90 @@
+#include "integrate.h"
+
+static inline int bad_args(integrand_f f, float *a, float *b, unsigned *n,
+                           float *out)
+{
+    return (f == NULL || out == NULL || *n == 0u || !(*b > *a));
+}
+
+integ_status_t midpoint(integrand_f f, void *ctx, float a, float b, unsigned n,
+                        float *out)
+{
+    /*check if all necessary parameters have been given */
+    if (bad_args(f, &a, &b, &n, out))
+        return INTEG_ERR_BAD_ARGS;
+
+    float sum = 0.0f;
+    float fx = 0.0f;
+
+    /*intervall width h: */
+    const float h = (b - a) / (float)n;
+    float x = a + 0.5f * h;
+
+    for (unsigned i = 0; i < n; ++i)
+    {
+        fx = f(x, ctx);
+        sum = sum + fx;
+        x = x + h;
+    }
+
+    *out = sum * h;
+    return INTEG_OK;
+}
+
+integ_status_t trapezoid(integrand_f f, void *ctx, float a, float b, unsigned n,
+                         float *out)
+{
+    /*check if all necessary parameters have been given */
+    if (bad_args(f, &a, &b, &n, out))
+    {
+        return INTEG_ERR_BAD_ARGS;
+    }
+
+    /*intervall width h: */
+    const float h = (b - a) / (float)n;
+    float sum = 0.5f * (f(a, ctx) + f(b, ctx));
+
+    float x = a + h;
+    for (unsigned i = 1; i < n; ++i)
+    {
+        sum = sum + f(x, ctx);
+        x = x + h;
+    }
+
+    *out = sum * h;
+    return INTEG_OK;
+}
+
+integ_status_t simpson(integrand_f f, void *ctx, float a, float b, unsigned n,
+                       float *out)
+{
+    /*check if all necessary parameters have been given */
+    if (bad_args(f, &a, &b, &n, out))
+    {
+        return INTEG_ERR_BAD_ARGS;
+    }
+    if (n & 1u) /*n must be even*/
+    {
+        return INTEG_ERR_N_EVEN_REQUIRED;
+    }
+
+    float sum_odd = 0.0f;
+    float sum_even = 0.0f;
+    /*intervall width h: */
+    const float h = (b - a) / (float)n;
+
+    float x = a + h;
+    for (unsigned i = 1; i < n; ++i)
+    {
+        const float fx = f(x, ctx);
+        if (i & 1u)
+            sum_odd = sum_odd + fx;
+        else
+            sum_even = sum_even + fx;
+        x = x + h;
+    }
+
+    *out =
+        (h / 3.0f) * (f(a, ctx) + 4.0f * sum_odd + 2.0f * sum_even + f(b, ctx));
+    return INTEG_OK;
+}