r/src/Rmoocore.c (matrix_transpose_double): Faster transpose.

Author: MLopez-Ibanez

r/src/Rmoocore.c

@@ -261,19 +261,23 @@ static inline void
 matrix_transpose_double(double * restrict dst, const double * restrict src,
                         const size_t nrows, const size_t ncols)
 {
-    ASSUME(nrows < SIZE_MAX/2 && ncols < SIZE_MAX/2);
-    if (nrows <= 0 || ncols <= 0)
+    // Make sure that nrows * (ncols + 1) < SIZE_MAX
+    ASSUME(nrows < SIZE_MAX / (ncols+1) && (ncols+1) < SIZE_MAX / nrows);
+    if (nrows == 0 || ncols == 0)
         return;
 
     const size_t len_1 = (nrows * ncols) - 1;
     size_t i = 0, j = 0;
     for (; j <= len_1; i++, j += nrows)
         dst[j] = src[i];
 
-    for (; i <= len_1; i++, j += nrows) {
-	    if (j > len_1) j -= len_1;
-	    dst[j] = src[i];
-	}
+    // FIXME: https://gcc.gnu.org/PR125293
+    j -= len_1;
+    while (i <= len_1) {
+        for (; j <= len_1; i++, j += nrows)
+            dst[j] = src[i];
+        j -= len_1;
+    }
 }
 
 SEXP