[04/12] RISC-V: memmove() size optimized version: Add comments
Commit Message
Since the algorithm in this version of memmove() is different
from the original version, add comments to give a description.
Reviewed-by: Christian Herber <christian.herber@oss.nxp.com>
Reviewed-by: Eric Salem <ericsalem@gmail.com>
Signed-off-by: m fally <marlene.fally@gmail.com>
---
newlib/libc/machine/riscv/memmove.S | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
Comments
LGTM
On Wed, Apr 9, 2025 at 2:49 PM m fally <marlene.fally@gmail.com> wrote:
>
> Since the algorithm in this version of memmove() is different
> from the original version, add comments to give a description.
>
> Reviewed-by: Christian Herber <christian.herber@oss.nxp.com>
> Reviewed-by: Eric Salem <ericsalem@gmail.com>
> Signed-off-by: m fally <marlene.fally@gmail.com>
> ---
> 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
>
@@ -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