move fvec_madd_* functions declarations to a right header (#3054)

Summary:
The implementations for `fvec_madd` and `fvec_madd_and_argmin` are in `utils/distances.cpp`, so I moved the declarations from `utils/utils.h` to `utils/distances.h`

Pull Request resolved: #3054

Reviewed By: mlomeli1

Differential Revision: D49687725

Pulled By: mdouze

fbshipit-source-id: b98c13f5710f06daba479767a7aab8d62d6e6ddf

faiss/utils/distances.h

@@ -434,4 +434,27 @@ void compute_PQ_dis_tables_dsub2(
  * Templatized versions of distance functions
  ***************************************************************************/
 
+/***************************************************************************
+ * Misc  matrix and vector manipulation functions
+ ***************************************************************************/
+
+/** compute c := a + bf * b for a, b and c tables
+ *
+ * @param n   size of the tables
+ * @param a   size n
+ * @param b   size n
+ * @param c   restult table, size n
+ */
+void fvec_madd(size_t n, const float* a, float bf, const float* b, float* c);
+
+/** same as fvec_madd, also return index of the min of the result table
+ * @return    index of the min of table c
+ */
+int fvec_madd_and_argmin(
+        size_t n,
+        const float* a,
+        float bf,
+        const float* b,
+        float* c);
+
 } // namespace faiss

faiss/utils/utils.h

@@ -49,25 +49,6 @@ uint64_t get_cycles();
  * Misc  matrix and vector manipulation functions
  ***************************************************************************/
 
-/** compute c := a + bf * b for a, b and c tables
- *
- * @param n   size of the tables
- * @param a   size n
- * @param b   size n
- * @param c   restult table, size n
- */
-void fvec_madd(size_t n, const float* a, float bf, const float* b, float* c);
-
-/** same as fvec_madd, also return index of the min of the result table
- * @return    index of the min of table c
- */
-int fvec_madd_and_argmin(
-        size_t n,
-        const float* a,
-        float bf,
-        const float* b,
-        float* c);
-
 /* perform a reflection (not an efficient implementation, just for test ) */
 void reflection(const float* u, float* x, size_t n, size_t d, size_t nu);