[PATCH v2 04/11] RISC-V: memmove() size optimized version: Add comments

Since the algorithm in this version of memmove() is different
from the original version, add comments to give a description.

Reviewed-by: Christian Herber <[email protected]>
Reviewed-by: Eric Salem <[email protected]>
Signed-off-by: m fally <[email protected]>
---
 newlib/libc/machine/riscv/memmove.S | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/newlib/libc/machine/riscv/memmove.S b/newlib/libc/machine/riscv/memmove.S
index a77ac44be..36fe00eba 100644
--- a/newlib/libc/machine/riscv/memmove.S
+++ b/newlib/libc/machine/riscv/memmove.S
@@ -14,21 +14,21 @@
 .global memmove
 .type	memmove, @function
 memmove:
-  beqz a2, .Ldone
+  beqz a2, .Ldone		/* in case there are 0 bytes to be copied, return immediately */
 
-  mv a4, a0
+  mv a4, a0			/* copy the destination address over to a4, since memmove should return that address in a0 at the end */
   li a3, 1
-  bgtu  a1, a0, .Lcopy
+  bgtu  a1, a0, .Lcopy		/* in case of source address > destination address, copy from start to end of the specified memory area */
 
-  li a3, -1
-  add   a4, a4, a2
-  add   a1, a1, a2
+  li a3, -1			/* otherwhise, we need to start copying from the end of the specified memory area, therefore after each copied byte, increment the addresses by -1 */
+  add   a4, a4, a2		/* add the number of bytes to be copied to both addresses. this gives an incorrect address, */
+  add   a1, a1, a2		/* therefore we need to subtract 1 from both addresses in the next step before starting the copying process. */
 
 .Lincrement:
-  add   a4, a4, a3
+  add   a4, a4, a3 		/* in case of source address < destination address, increment both addresses by -1 before copying any data to obtain the correct start addresses */
   add   a1, a1, a3
 .Lcopy:
-  lb a5, 0(a1)
+  lb a5, 0(a1)			/* copy bytes as long as a2 (= the number of bytes to be copied) > 0 */
   sb a5, 0(a4)
   add   a2, a2, -1
   bnez a2, .Lincrement
-- 
2.49.0