evalexpr: initial recursive descent parser

src/eval/eval.c

@@ -0,0 +1,69 @@
+#include "eval.h"
+
+#define UNREACHABLE() __builtin_unreachable()
+
+static int my_pow(int lhs, int rhs)
+{
+    if (!rhs)
+        return 1;
+    int rec = my_pow(lhs * lhs, rhs / 2);
+    if (rhs & 1)
+        rec *= lhs;
+    return rec;
+}
+
+static int my_fact(int num)
+{
+    int ret = 1;
+    while (num > 1)
+        ret *= num--;
+    return ret;
+}
+
+static int eval_unop(const struct unop_node *un_op)
+{
+    switch (un_op->op)
+    {
+    case UNOP_IDENTITY:
+        return eval_ast(un_op->tree);
+    case UNOP_NEGATE:
+        return -eval_ast(un_op->tree);
+    case UNOP_FACT:
+        return my_fact(eval_ast(un_op->tree));
+    }
+    UNREACHABLE();
+}
+
+static int eval_binop(const struct binop_node *bin_op)
+{
+#define EVAL_OP(OP, TREE) (eval_ast((TREE)->lhs) OP eval_ast((TREE)->rhs))
+    switch (bin_op->op)
+    {
+    case BINOP_PLUS:
+        return EVAL_OP(+, bin_op);
+    case BINOP_MINUS:
+        return EVAL_OP(-, bin_op);
+    case BINOP_TIMES:
+        return EVAL_OP(*, bin_op);
+    case BINOP_DIVIDES:
+        return EVAL_OP(/, bin_op);
+    case BINOP_POW:
+        return my_pow(eval_ast(bin_op->lhs), eval_ast(bin_op->rhs));
+    }
+#undef EVAL_OP
+    UNREACHABLE();
+}
+
+int eval_ast(const struct ast_node *ast)
+{
+    switch (ast->kind)
+    {
+    case NODE_NUM:
+        return ast->val.num;
+    case NODE_UNOP:
+        return eval_unop(&ast->val.un_op);
+    case NODE_BINOP:
+        return eval_binop(&ast->val.bin_op);
+    }
+    UNREACHABLE();
+}

src/eval/eval.h

@@ -0,0 +1,8 @@
+#ifndef EVAL_H
+#define EVAL_H
+
+#include "ast/ast.h"
+
+int eval_ast(const struct ast_node *ast);
+
+#endif /* !EVAL_H */