1 files changed, 73 insertions, 0 deletions
diff --git a/src/expr.c b/src/expr.c
new file mode 100644
index 0000000..a808232
--- /dev/null
+++ b/src/expr.c
@@ -0,0 +1,73 @@
+#include <math.h>
+#include "expr.h"
+
+double expr_eval(struct expr *expr, double time)
+{
+    switch (expr->type) {
+        case EXPR_NUMBER: return expr->number;
+        case EXPR_TIME: return time;
+        case EXPR_OP: {
+            size_t n_args = expr->op.args.len;
+            double args[n_args];
+            for (size_t i = 0; i < n_args; i++)
+                args[i] = expr_eval(&expr->op.args.ptr[i], time);
+            double accum;
+            switch (expr->op.type) {
+                case OP_ADD:
+                    accum = 0.0;
+                    for (size_t i = 0; i < n_args; i++)
+                        accum += args[i];
+                    return accum;
+                case OP_SUB:
+                    if (n_args == 1) return -args[0];
+                    return args[0] - args[1];
+                case OP_MUL:
+                    accum = 1.0;
+                    for (size_t i = 0; i < n_args; i++)
+                        accum *= args[i];
+                    return accum;
+                case OP_DIV:
+                    if (n_args == 1) return 1.0 / args[0];
+                    return args[0] / args[1];
+                case OP_MOD:
+                    return fmod(args[0], args[1]);
+                case OP_MIN:
+                    for (size_t i = 0; i < n_args; i++)
+                        if (i == 0 || args[i] < accum)
+                            accum = args[i]; 
+                    return accum;
+                case OP_MAX:
+                    for (size_t i = 0; i < n_args; i++)
+                        if (i == 0 || args[i] > accum)
+                            accum = args[i]; 
+                    return accum;
+                case OP_CLAMP:
+                    if (args[0] < args[1]) return args[1];
+                    if (args[0] > args[2]) return args[2];
+                    return args[0];
+                case OP_MIX:
+                    return args[0] + (args[1] - args[0]) * args[2];
+                case OP_ABS:
+                    return fabs(args[0]);
+                default: break; // unreachable
+            }
+        }
+    }
+    return 0.0;
+}
+
+void expr_free(struct expr *expr)
+{
+    if (expr->type == EXPR_OP) {
+        for (size_t i = 0; i < expr->op.args.len; i++)
+            expr_free(&expr->op.args.ptr[i]);
+        free(expr->op.args.ptr);
+    }
+}
+
+void expr_copy(struct expr *dst, struct expr *src)
+{
+    *dst = *src;
+    if (src->type == EXPR_OP)
+        array_dup(&dst->op.args, &src->op.args);
+}