Re: [PATCH] crypto: x86/curve25519 - Remove unused carry variables

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Hi Herbert,

On Thu, Jul 23, 2020 at 9:51 AM Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> wrote:
>
> The carry variables are assigned but never used, which upsets
> the compiler.  This patch removes them.
>
> Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
>
> diff --git a/arch/x86/crypto/curve25519-x86_64.c b/arch/x86/crypto/curve25519-x86_64.c
> index 8a17621f7d3a..8acbb6584a37 100644
> --- a/arch/x86/crypto/curve25519-x86_64.c
> +++ b/arch/x86/crypto/curve25519-x86_64.c
> @@ -948,10 +948,8 @@ static void store_felem(u64 *b, u64 *f)
>  {
>         u64 f30 = f[3U];
>         u64 top_bit0 = f30 >> (u32)63U;
> -       u64 carry0;
>         u64 f31;
>         u64 top_bit;
> -       u64 carry;
>         u64 f0;
>         u64 f1;
>         u64 f2;
> @@ -970,11 +968,11 @@ static void store_felem(u64 *b, u64 *f)
>         u64 o2;
>         u64 o3;
>         f[3U] = f30 & (u64)0x7fffffffffffffffU;
> -       carry0 = add_scalar(f, f, (u64)19U * top_bit0);
> +       add_scalar(f, f, (u64)19U * top_bit0);
>         f31 = f[3U];
>         top_bit = f31 >> (u32)63U;
>         f[3U] = f31 & (u64)0x7fffffffffffffffU;
> -       carry = add_scalar(f, f, (u64)19U * top_bit);
> +       add_scalar(f, f, (u64)19U * top_bit);
>         f0 = f[0U];
>         f1 = f[1U];
>         f2 = f[2U];
> --

That seems obvious and reasonable, and so I'm inclined to ack this,
but I first wanted to give Karthik (CC'd) a chance to chime in here,
as it's his HACL* project that's responsible, and he might have some
curious insight.

Jason



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