From af6c47ef2835e6e258a000a4cbe40e6a1dbc5bd6 Mon Sep 17 00:00:00 2001
From: Lewis Van Winkle <lv@codeplea.com>
Date: Mon, 22 Aug 2016 21:20:28 -0500
Subject: [PATCH] Added option TE_POW_FROM_RIGHT

---
 test.c     | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 tinyexpr.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+)

diff --git a/test.c b/test.c
index 59941f0..21d270f 100644
--- a/test.c
+++ b/test.c
@@ -32,6 +32,10 @@ typedef struct {
     double answer;
 } test_case;
 
+typedef struct {
+    const char *expr1;
+    const char *expr2;
+} test_equ;
 
 
 
@@ -517,6 +521,52 @@ void test_optimize() {
     }
 }
 
+void test_pow() {
+#ifdef TE_POW_FROM_RIGHT
+    test_equ cases[] = {
+        {"2^3^4", "2^(3^4)"},
+        {"2^1.1^1.2^1.3", "2^(1.1^(1.2^1.3))"},
+        {"-a^b", "-(a^b)"},
+        {"-a^-b", "-(a^-b)"}
+    };
+#else
+    test_equ cases[] = {
+        {"2^3^4", "(2^3)^4"},
+        {"2^1.1^1.2^1.3", "((2^1.1)^1.2)^1.3"},
+        {"-a^b", "(-a)^b"},
+        {"-a^-b", "(-a)^(-b)"}
+    };
+#endif
+
+    double a = 2, b = 3;
+
+    te_variable lookup[] = {
+        {"a", &a},
+        {"b", &b}
+    };
+
+    int i;
+    for (i = 0; i < sizeof(cases) / sizeof(test_equ); ++i) {
+        const char *expr1 = cases[i].expr1;
+        const char *expr2 = cases[i].expr2;
+
+        te_expr *ex1 = te_compile(expr1, lookup, sizeof(lookup)/sizeof(te_variable), 0);
+        te_expr *ex2 = te_compile(expr2, lookup, sizeof(lookup)/sizeof(te_variable), 0);
+
+        lok(ex1);
+        lok(ex2);
+
+        double r1 = te_eval(ex1);
+        double r2 = te_eval(ex2);
+
+        fflush(stdout);
+        lfequal(r1, r2);
+
+        te_free(ex1);
+        te_free(ex2);
+    }
+
+}
 
 int main(int argc, char *argv[])
 {
@@ -528,6 +578,7 @@ int main(int argc, char *argv[])
     lrun("Dynamic", test_dynamic);
     lrun("Closure", test_closure);
     lrun("Optimize", test_optimize);
+    lrun("Pow", test_pow);
     lresults();
 
     return lfails != 0;
diff --git a/tinyexpr.c b/tinyexpr.c
index 0246580..9021cab 100644
--- a/tinyexpr.c
+++ b/tinyexpr.c
@@ -22,6 +22,14 @@
  * 3. This notice may not be removed or altered from any source distribution.
  */
 
+/* COMPILE TIME OPTIONS */
+
+/* Exponentiation associativity:
+For a^b^c = (a^b)^c and -a^b = (-a)^b do nothing.
+For a^b^c = a^(b^c) and -a^b = -(a^b) uncomment the next line.*/
+/* #define TE_POW_FROM_RIGHT */
+
+
 #include "tinyexpr.h"
 #include <stdlib.h>
 #include <math.h>
@@ -357,7 +365,48 @@ static te_expr *power(state *s) {
     return ret;
 }
 
+#ifdef TE_POW_FROM_RIGHT
+static te_expr *factor(state *s) {
+    /* <factor>    =    <power> {"^" <power>} */
+    te_expr *ret = power(s);
 
+    int neg = 0;
+    te_expr *insertion = 0;
+
+    if (ret->type == (TE_FUNCTION1 | TE_FLAG_PURE) && ret->function == negate) {
+        te_expr *se = ret->parameters[0];
+        if (se->type != TE_CONSTANT) {
+            free(ret);
+            ret = se;
+            neg = 1;
+        }
+    }
+
+    while (s->type == TOK_INFIX && (s->function == pow)) {
+        te_fun2 t = s->function;
+        next_token(s);
+
+        if (insertion) {
+            /* Make exponentiation go right-to-left. */
+            te_expr *insert = NEW_EXPR(TE_FUNCTION2 | TE_FLAG_PURE, insertion->parameters[1], power(s));
+            insert->function = t;
+            insertion->parameters[1] = insert;
+            insertion = insert;
+        } else {
+            ret = NEW_EXPR(TE_FUNCTION2 | TE_FLAG_PURE, ret, power(s));
+            ret->function = t;
+            insertion = ret;
+        }
+    }
+
+    if (neg) {
+        ret = NEW_EXPR(TE_FUNCTION1 | TE_FLAG_PURE, ret);
+        ret->function = negate;
+    }
+
+    return ret;
+}
+#else
 static te_expr *factor(state *s) {
     /* <factor>    =    <power> {"^" <power>} */
     te_expr *ret = power(s);
@@ -371,6 +420,8 @@ static te_expr *factor(state *s) {
 
     return ret;
 }
+#endif
+
 
 
 static te_expr *term(state *s) {