Re: [Acx100-devel] [PATCH] acx: make firmware statistics parsing more intelligent

[Denis V. <vd...@il...>]

On Friday 03 February 2006 12:58, Andreas Mohr wrote:
> -=A0=A0=A0=A0=A0=A0=A0adev->tx_head =3D (head + 1) % TX_CNT;
> +=A0=A0=A0=A0=A0=A0=A0/* slower: adev->tx_head =3D (head + 1) % TX_CNT; */
> +=A0=A0=A0=A0=A0=A0=A0adev->tx_head =3D head + 1;
> +=A0=A0=A0=A0=A0=A0=A0if (adev->tx_head >=3D TX_CNT)
> +=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0adev->tx_head =3D 0;


struct a {
    int tx_head;
};

#define TX_CNT 16

void f(struct a *adev, int head) {
    adev->tx_head =3D (head + 1) % TX_CNT;
}

void g(struct a *adev, int head) {
    adev->tx_head =3D head + 1;
    if (adev->tx_head >=3D TX_CNT)
        adev->tx_head =3D 0;
}


gcc -Os -S t.c -fomit-frame-pointer -falign-functions=3D1 -falign-labels=3D=
1 -falign-loops=3D1 -falign-jumps=3D1 -mtune=3Di386 -march=3Di386
produces:

f:
        movl    8(%esp), %eax
        incl    %eax
        movl    $16, %edx
        movl    %edx, %ecx
        cltd
        idivl   %ecx
        movl    4(%esp), %eax
        movl    %edx, (%eax)
        ret
        .size   f, .-f
=2Eglobl g
        .type   g, @function
g:
        movl    4(%esp), %edx
        movl    8(%esp), %eax
        incl    %eax
        movl    %eax, (%edx)
        cmpl    $15, %eax
        jle     .L6
        movl    $0, (%edx)
=2EL6:
        ret
        .size   g, .-g
        .ident  "GCC: (GNU) 4.0.0"

Well, gcc obviously failed to realize that "% 16" =3D=3D "& 15".
I'll file a bug. Meanwhile, with & 15 f() is better:

f:
        movl    8(%esp), %eax
        incl    %eax
        andl    $15, %eax
        movl    4(%esp), %edx
        movl    %eax, (%edx)
        ret
        .size   f, .-f
=2Eglobl g
        .type   g, @function
g:
        movl    4(%esp), %edx
        movl    8(%esp), %eax
        incl    %eax
        movl    %eax, (%edx)
        cmpl    $15, %eax
        jle     .L6
        movl    $0, (%edx)
=2EL6:
        ret
        .size   g, .-g
        .ident  "GCC: (GNU) 4.0.0"

=2D-
vda