fixing pow<>

0^0 now correclty yields 1
brunocodutra · Apr 11, 2016 · 5044e9a · 5044e9a
1 parent 64f0775
commit 5044e9a
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Showing 3 changed files with 35 additions and 13 deletions.
diff --git a/example/src/number/arithmetic.cpp b/example/src/number/arithmetic.cpp
@@ -108,7 +108,6 @@ using x = metal::pow_t<
 >;
 
 static_assert(std::is_same<x, metal::number<long, -16807>>::value, "");
-static_assert(!metal::is_just</**/metal::pow</**/metal::integer<0>, metal::integer<0>>>::value, "");
 static_assert(!metal::is_just</**/metal::pow</**/metal::integer<0>, metal::integer<-3>>>::value, "");
 /// [pow]
 }
diff --git a/include/metal/number/arithmetic/pow.hpp b/include/metal/number/arithmetic/pow.hpp
@@ -68,12 +68,10 @@ namespace metal
     namespace detail
     {
         template<typename T>
-        constexpr T pow_impl(T base, T exp, T result = 1){
-            return !exp ?
-                result :
-                exp < 0 ?
-                    pow_impl(1/(base*base), -exp/2, -exp%2 ? result/base : result) :
-                    pow_impl(base*base, exp/2, exp%2 ? result*base : result);
+        constexpr T pow_impl(T base, T exp, T result = 1) {
+            return exp == 1 ?
+                base*result :
+                pow_impl(base*base, exp/2, exp%2 ? result*base : result);
         }
 
         template<typename... nums>
@@ -87,19 +85,43 @@ namespace metal
 
         template<typename tx, tx vx, typename ty, ty vy, typename... nums>
         struct pow<number<tx, vx>, number<ty, vy>, nums...> :
-            pow<
-                number<decltype(vx*vy), pow_impl<decltype(vx*vy)>(vx, vy)>,
-                nums...
+            conditional<
+                boolean<vy < 0>,
+                pow<number<decltype(vx*vy), 0>, nums...>,
+                pow<
+                    number<decltype(vx*vy), pow_impl<decltype(vx*vy)>(vx, vy)>,
+                    nums...
+                >
             >
         {};
 
         template<typename tx, typename ty, ty vy, typename... nums>
         struct pow<number<tx, tx(0)>, number<ty, vy>, nums...> :
             conditional<
                 boolean<(vy > 0)>,
-                pow<number<decltype(tx(0)*vy), 0>, nums...>
+                pow<number<decltype(tx()*vy), 0>, nums...>
             >
         {};
+
+        template<typename tx, typename ty, ty vy, typename... nums>
+        struct pow<number<tx, tx(1)>, number<ty, vy>, nums...> :
+            pow<number<decltype(tx()*vy), 1>, nums...>
+        {};
+
+        template<typename tx, tx vx, typename ty, typename... nums>
+        struct pow<number<tx, vx>, number<ty, ty(0)>, nums...> :
+            pow<number<decltype(vx*ty()), 1>, nums...>
+        {};
+
+        template<typename tx, typename ty, typename... nums>
+        struct pow<number<tx, tx(0)>, number<ty, ty(0)>, nums...> :
+            pow<number<decltype(tx()*ty()), 1>, nums...>
+        {};
+
+        template<typename tx, typename ty, typename... nums>
+        struct pow<number<tx, tx(1)>, number<ty, ty(0)>, nums...> :
+            pow<number<decltype(tx()*ty()), 1>, nums...>
+        {};
     }
 }
 

diff --git a/test/src/metal/number/arithmetic.cpp b/test/src/metal/number/arithmetic.cpp
@@ -36,8 +36,8 @@
     ASSERT((metal::is_just_t<metal::pow<NUMS(N)>>), (BOOL(N > 0))); \
     ASSERT((metal::is_just_t<metal::div<NUMS(M) COMMA(AND(M, N)) NUMS(N)>>), (BOOL(!M ^ !N))); \
     ASSERT((metal::is_just_t<metal::mod<NUMS(M) COMMA(AND(M, N)) NUMS(N)>>), (BOOL(!M ^ !N))); \
-    ASSERT((metal::is_just_t<metal::pow<NUMS(M) COMMA(AND(M, N)) NUMS(N)>>), (BOOL(!M ^ !N))); \
-    ASSERT((metal::is_just_t<metal::pow<NUMS(M) COMMA(M) metal::integer<-N>>>), (BOOL(!M))); \
+    ASSERT((metal::is_just_t<metal::pow<NUMS(M) COMMA(AND(M, N)) NUMS(N)>>), (BOOL(M || N))); \
+    ASSERT((metal::is_just_t<metal::pow<NUMS(M) COMMA(M) metal::integer<-N>>>), (BOOL(!M || !N))); \
     ASSERT((metal::equal_to_t<metal::neg_t<metal::neg_t<NUM(N)>>, NUM(N)>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::inc_t<NUM(N)>, NUM(INC(N))>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::dec_t<NUM(INC(N))>, NUM(N)>), (TRUE)); \
@@ -52,6 +52,7 @@
     ASSERT((metal::equal_to_t<metal::mod_t<NUMS(INC(N))>, NUM(0)>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::pow_t<NUMS(INC(N))>, NUM(0)>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::add_t<metal::mul_t<metal::div_t<NUM(M), NUM(INC(N))>, NUM(INC(N))>, metal::mod_t<NUM(M), NUM(INC(N))>>, NUM(M)>), (TRUE)); \
+    ASSERT((metal::equal_to_t<metal::pow_t<NUM(0) COMMA(N) NUMS(N)>, metal::integer<!!N>>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::pow_t<NUM(1) COMMA(N) NUMS(N)>, NUM(1)>), (TRUE)); \
     ASSERT((metal::equal_to_t<metal::pow_t<NUM(2), NUM(N)>, metal::integer<1 << N>>), (TRUE)); \
 /**/