[PATCH for-6.1?] bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")

[PATCH for-6.1?] bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")

[Mark Cave-Ayland]

Commit db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation") introduced a
bitrev8() function to reverse the bit ordering required for storing the MAC
address in the q800 PROM.

This function is not required since QEMU implements its own revbit8() function
which does exactly the same thing. Remove the extraneous bitrev8() function and
switch its only caller in hw/m68k/q800.c to use revbit8() instead.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
---
 hw/m68k/q800.c        |  2 +-
 include/qemu/bitops.h | 22 ----------------------
 2 files changed, 1 insertion(+), 23 deletions(-)

---
I picked this up reading the loongarch thread where I realised that QEMU
already has a revbit8() function - I was searching for bitrev8() before
deciding that this needed to be added since this was the name of the equivalent
function in Linux.

I think this is a good candidate for 6.1 still because a) it only has 1 caller
which is easy for me to test and b) it prevents anyone else coming along and
accidentally using it later.

MCA. 

diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
index 6817c8b5d1..ac0a13060b 100644
--- a/hw/m68k/q800.c
+++ b/hw/m68k/q800.c
@@ -334,7 +334,7 @@ static void q800_init(MachineState *machine)
     prom = memory_region_get_ram_ptr(dp8393x_prom);
     checksum = 0;
     for (i = 0; i < 6; i++) {
-        prom[i] = bitrev8(nd_table[0].macaddr.a[i]);
+        prom[i] = revbit8(nd_table[0].macaddr.a[i]);
         checksum ^= prom[i];
     }
     prom[7] = 0xff - checksum;
diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h
index 110c56e099..03213ce952 100644
--- a/include/qemu/bitops.h
+++ b/include/qemu/bitops.h
@@ -618,26 +618,4 @@ static inline uint64_t half_unshuffle64(uint64_t x)
     return x;
 }
 
-/**
- * bitrev8:
- * @x: 8-bit value to be reversed
- *
- * Given an input value with bits::
- *
- *   ABCDEFGH
- *
- * return the value with its bits reversed from left to right::
- *
- *   HGFEDCBA
- *
- * Returns: the bit-reversed value.
- */
-static inline uint8_t bitrev8(uint8_t x)
-{
-    x = ((x >> 1) & 0x55) | ((x << 1) & 0xaa);
-    x = ((x >> 2) & 0x33) | ((x << 2) & 0xcc);
-    x = (x >> 4) | (x << 4) ;
-    return x;
-}
-
 #endif
-- 
2.20.1

Re: [PATCH for-6.1?] bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")

[Richard Henderson]

On 7/25/21 1:05 AM, Mark Cave-Ayland wrote:
> Commit db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation") introduced a
> bitrev8() function to reverse the bit ordering required for storing the MAC
> address in the q800 PROM.
> 
> This function is not required since QEMU implements its own revbit8() function
> which does exactly the same thing. Remove the extraneous bitrev8() function and
> switch its only caller in hw/m68k/q800.c to use revbit8() instead.
> 
> Signed-off-by: Mark Cave-Ayland<mark.cave-ayland@ilande.co.uk>
> ---
>   hw/m68k/q800.c        |  2 +-
>   include/qemu/bitops.h | 22 ----------------------
>   2 files changed, 1 insertion(+), 23 deletions(-)
> 
> ---
> I picked this up reading the loongarch thread where I realised that QEMU
> already has a revbit8() function - I was searching for bitrev8() before
> deciding that this needed to be added since this was the name of the equivalent
> function in Linux.
> 
> I think this is a good candidate for 6.1 still because a) it only has 1 caller
> which is easy for me to test and b) it prevents anyone else coming along and
> accidentally using it later.
> 
> MCA.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~

Re: [PATCH for-6.1?] bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")

[Philippe Mathieu-Daudé]

On 7/25/21 1:05 PM, Mark Cave-Ayland wrote:
> Commit db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation") introduced a
> bitrev8() function to reverse the bit ordering required for storing the MAC
> address in the q800 PROM.
> 
> This function is not required since QEMU implements its own revbit8() function
> which does exactly the same thing. Remove the extraneous bitrev8() function and
> switch its only caller in hw/m68k/q800.c to use revbit8() instead.
> 
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
> ---
>  hw/m68k/q800.c        |  2 +-
>  include/qemu/bitops.h | 22 ----------------------
>  2 files changed, 1 insertion(+), 23 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Re: [PATCH for-6.1?] bitops.h: revert db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation")

[Richard Henderson]

On 7/25/21 1:05 AM, Mark Cave-Ayland wrote:
> Commit db1ffc32dd ("qemu/bitops.h: add bitrev8 implementation") introduced a
> bitrev8() function to reverse the bit ordering required for storing the MAC
> address in the q800 PROM.
> 
> This function is not required since QEMU implements its own revbit8() function
> which does exactly the same thing. Remove the extraneous bitrev8() function and
> switch its only caller in hw/m68k/q800.c to use revbit8() instead.
> 
> Signed-off-by: Mark Cave-Ayland<mark.cave-ayland@ilande.co.uk>
> ---
>   hw/m68k/q800.c        |  2 +-
>   include/qemu/bitops.h | 22 ----------------------
>   2 files changed, 1 insertion(+), 23 deletions(-)
> 
> ---
> I picked this up reading the loongarch thread where I realised that QEMU
> already has a revbit8() function - I was searching for bitrev8() before
> deciding that this needed to be added since this was the name of the equivalent
> function in Linux.
> 
> I think this is a good candidate for 6.1 still because a) it only has 1 caller
> which is easy for me to test and b) it prevents anyone else coming along and
> accidentally using it later.
> 
> MCA.

Queued for 6.1.


r~