mesa: Add _mesa_swap2_copy and _mesa_swap4_copy

We have _mesa_swap{2,4} but these do in-place byte-swapping only. The new
functions receive an extra parameter so we can swap bytes on a source
input array and store the results in a (possibly different) destination
array.

This is useful to implement byte-swapping in pixel uploads, since in this
case we need to swap bytes on the src data which is owned by the
application so we can't do an in-place byte swap.

v2:
  - Include compiler.h in image.h, which is necessary to build in MSCV as
    indicated by Brian Paul.

Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>

2 files changed, 32 insertions, 10 deletions

diff --git a/src/mesa/main/image.c b/src/mesa/main/image.c
index 4ea5f04c986..9ad97c56e40 100644
--- a/src/mesa/main/image.c
+++ b/src/mesa/main/image.c
@@ -41,36 +41,45 @@
 
 
 /**
- * Flip the order of the 2 bytes in each word in the given array.
+ * Flip the order of the 2 bytes in each word in the given array (src) and
+ * store the result in another array (dst). For in-place byte-swapping this
+ * function can be called with the same array for src and dst.
  *
- * \param p array.
+ * \param dst the array where byte-swapped data will be stored.
+ * \param src the array with the source data we want to byte-swap.
  * \param n number of words.
  */
 void
-_mesa_swap2( GLushort *p, GLuint n )
+_mesa_swap2_copy( GLushort *dst, GLushort *src, GLuint n )
 {
    GLuint i;
    for (i = 0; i < n; i++) {
-      p[i] = (p[i] >> 8) | ((p[i] << 8) & 0xff00);
+      dst[i] = (src[i] >> 8) | ((src[i] << 8) & 0xff00);
    }
 }
 
 
 
 /*
- * Flip the order of the 4 bytes in each word in the given array.
+ * Flip the order of the 4 bytes in each word in the given array (src) and
+ * store the result in another array (dst). For in-place byte-swapping this
+ * function can be called with the same array for src and dst.
+ *
+ * \param dst the array where byte-swapped data will be stored.
+ * \param src the array with the source data we want to byte-swap.
+ * \param n number of words.
  */
 void
-_mesa_swap4( GLuint *p, GLuint n )
+_mesa_swap4_copy( GLuint *dst, GLuint *src, GLuint n )
 {
    GLuint i, a, b;
    for (i = 0; i < n; i++) {
-      b = p[i];
+      b = src[i];
       a =  (b >> 24)
 	| ((b >> 8) & 0xff00)
 	| ((b << 8) & 0xff0000)
 	| ((b << 24) & 0xff000000);
-      p[i] = a;
+      dst[i] = a;
    }
 }
 
diff --git a/src/mesa/main/image.h b/src/mesa/main/image.h
index abd84bf2f87..44863cc5927 100644
--- a/src/mesa/main/image.h
+++ b/src/mesa/main/image.h
@@ -28,15 +28,28 @@
 
 
 #include "glheader.h"
+#include "compiler.h"
 
 struct gl_context;
 struct gl_pixelstore_attrib;
 
 extern void
-_mesa_swap2( GLushort *p, GLuint n );
+_mesa_swap2_copy(GLushort *dst, GLushort *src, GLuint n);
 
 extern void
-_mesa_swap4( GLuint *p, GLuint n );
+_mesa_swap4_copy(GLuint *dst, GLuint *src, GLuint n);
+
+static inline void
+_mesa_swap2(GLushort *p, GLuint n)
+{
+   _mesa_swap2_copy(p, p, n);
+}
+
+static inline void
+_mesa_swap4(GLuint *p, GLuint n)
+{
+   _mesa_swap4_copy(p, p, n);
+}
 
 extern GLintptr
 _mesa_image_offset( GLuint dimensions,