Add mempcpy implementation

A GNU extension that returns dst + size instead of dst. It's a nice
shortcut when copying strings with a known size or back-to-back blocks
and you have to do it often.

May of course be called directly or alternately through
__builtin_mempcpy in some compiler versions.

For ASM on native targets, it is implemented as an alternate entrypoint
to memcpy which adds minimal code and overhead.

Change-Id: I4cbb3483f6df3c1007247fe0a95fd7078737462b

1 files changed, 10 insertions, 0 deletions

diff --git a/firmware/asm/m68k/memcpy.S b/firmware/asm/m68k/memcpy.S
index 9762e31e02..a88ac3d091 100644
--- a/firmware/asm/m68k/memcpy.S
+++ b/firmware/asm/m68k/memcpy.S
@@ -27,6 +27,8 @@
     .global memcpy
     .global __memcpy_fwd_entry
     .type   memcpy,@function
+    .global mempcpy
+    .type   mempcpy,@function
 
 /* Copies <length> bytes of data in memory from <source> to <dest>
  * This version is optimized for speed
@@ -53,6 +55,14 @@
  * long+3) it writes longwords only. Same goes for word aligned destinations
  * if FULLSPEED is undefined.
  */
+mempcpy:
+    move.l  (4,%sp),%a1     /* Destination */
+    move.l  (8,%sp),%a0     /* Source */
+    move.l  (12,%sp),%d1    /* Length */
+
+    add.l   %d1,(4,%sp)     /* retval=Destination + Length */
+    bra.b   __memcpy_fwd_entry
+
 memcpy:
     move.l  (4,%sp),%a1     /* Destination */
     move.l  (8,%sp),%a0     /* Source */