From ee2d8d1e9d35235697d3066469d91c09f0477283 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sun, 8 Nov 2020 18:42:16 +0100
Subject: [PATCH] pratt: eval: add exponentiation operator

This showcases right-associative operators
---
 src/eval.c        | 19 +++++++++++++++++++
 src/operators.inc | 14 ++++++++------
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/src/eval.c b/src/eval.c
index 21a43aa..89afc7a 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -38,6 +38,8 @@ struct token {
     LeftFunc(Name)
 #define INFIX(Name)  \
     LeftFunc(Name)
+#define POWER(Name)  \
+    LeftFunc(Name)
 #define TERN(Name)  \
     LeftFunc(Name)
 #define PAREN(Name) \
@@ -72,6 +74,8 @@ static const struct {
     [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NulFunc(Name), LeftFunc(Name), },
 #define INFIX(Name, NulPrio, LeftPrio, ...)  \
     [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, LeftFunc(Name), },
+#define POWER(Name, NulPrio, LeftPrio, ...)  \
+    [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, LeftFunc(Name), },
 #define TERN(Name, NulPrio, LeftPrio, ...)  \
     [Name] = {OP_STRING(__VA_ARGS__), OP_SIZE(__VA_ARGS__), NulPrio, LeftPrio, NULL, LeftFunc(Name), },
 #define PAREN(Name, NulPrio, LeftPrio, ...) \
@@ -244,6 +248,21 @@ bool eval_string(const char *input, int *res) {
         *res = lhs Operator *res; \
         return true; \
     }
+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;
+}
+#define POWER(Name, NulPrio, LeftPrio, Operator) \
+    LeftFunc(Name) { \
+        if (!parse_until(input, res, LeftPrio - 1)) \
+            return false; \
+        *res = my_pow(lhs, *res); \
+        return true; \
+    }
 #define TERN(Name, NulPrio, LeftPrio, Operator) \
     LeftFunc(Name) { \
         int true_val; \
diff --git a/src/operators.inc b/src/operators.inc
index 08b217e..6efed95 100644
--- a/src/operators.inc
+++ b/src/operators.inc
@@ -8,12 +8,13 @@
 #endif
 
 // Simple operators
-OP(  PLUS_PLUS, 120, 110, PREFIX_POSTFIX,          ++, '+', '+', 0)
-OP(MINUS_MINUS, 120, 110, PREFIX_POSTFIX,          --, '-', '-', 0)
-OP(        NOT, 120,  -1,         PREFIX,           !, '!', 0)
-OP(    BIT_NOT, 120,  -1,         PREFIX,           ~, '~', 0)
-OP(       PLUS, 110,  90,   PREFIX_INFIX,           +, '+', 0)
-OP(      MINUS, 110,  90,   PREFIX_INFIX,           -, '-', 0)
+OP(  PLUS_PLUS, 130, 120, PREFIX_POSTFIX,          ++, '+', '+', 0)
+OP(MINUS_MINUS, 130, 120, PREFIX_POSTFIX,          --, '-', '-', 0)
+OP(        NOT, 130,  -1,         PREFIX,           !, '!', 0)
+OP(    BIT_NOT, 130,  -1,         PREFIX,           ~, '~', 0)
+OP(       PLUS, 120,  90,   PREFIX_INFIX,           +, '+', 0)
+OP(      MINUS, 120,  90,   PREFIX_INFIX,           -, '-', 0)
+OP(       POWER, -1, 110,          POWER, PLACEHOLDER, '*', '*', 0)
 OP(       TIMES, -1, 100,          INFIX,           *, '*', 0)
 OP(     DIVIDES, -1, 100,          INFIX,           /, '/', 0)
 OP(      MODULO, -1, 100,          INFIX,           %, '%', 0)
@@ -40,6 +41,7 @@ OP(      NUMBER,  0,  -1,         NOT_OP, PLACEHOLDER, 0)
 #undef PREFIX
 #undef PREFIX_INFIX
 #undef INFIX
+#undef POWER
 #undef TERN
 #undef PAREN
 #undef NOT_OP