Re: [Qemu-devel] [PATCH v6 17/24] qemu/bitops.h: add the bit ordering reversal functions stolen from linux

[Paolo Bonzini]

Il 06/03/2013 08:27, Kuo-Jung Su ha scritto:
> Signed-off-by: Kuo-Jung Su <address@hidden>
> ---
>  include/qemu/bitops.h |   63 
> ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 62 insertions(+), 1 deletion(-)
> 
> diff --git a/include/qemu/bitops.h b/include/qemu/bitops.h
> index affcc96..920d028 100644
> --- a/include/qemu/bitops.h
> +++ b/include/qemu/bitops.h
> @@ -3,7 +3,8 @@
>   *
>   * Copyright (C) 2010 Corentin Chary <address@hidden>
>   *
> - * Mostly inspired by (stolen from) linux/bitmap.h and linux/bitops.h
> + * Mostly inspired by (stolen from) linux/bitmap.h, linux/bitops.h
> + * and linux/bitrev.h
>   *
>   * This work is licensed under the terms of the GNU LGPL, version 2.1 or 
> later.
>   * See the COPYING.LIB file in the top-level directory.
> @@ -273,4 +274,64 @@ static inline uint64_t deposit64(uint64_t value, int 
> start, int length,
>      return (value & ~mask) | ((fieldval << start) & mask);
>  }
>  
> +/**
> + * bitrev8:
> + * @value: the value to reverse bit ordering from
> + *
> + * Reverse the 8 bit input @value
> + *
> + * Returns: the input @value with reversed bit ordering
> + */
> +static inline uint8_t bitrev8(uint8_t value)
> +{
> +    int i;
> +    uint8_t ret = 0;
> +    for (i = 0; i < 8; ++i) {
> +        if (value & BIT(i)) {
> +            ret |= BIT(7 - i);
> +        }
> +    }

Please use instead

   value = ((value & 0xAA) >> 1) | ((value & 0x55) << 1);
   value = ((value & 0xCC) >> 2) | ((value & 0x33) << 2);
   value = ((value & 0xF0) >> 4) | ((value & 0x0F) << 4);
   return value;

Paolo

> +    return ret;
> +}
> +
> +/**
> + * bitrev16:
> + * @value: the value to reverse bit ordering from
> + *
> + * Reverse the 16 bit input @value
> + *
> + * Returns: the input @value with reversed bit ordering
> + */
> +static inline uint16_t bitrev16(uint16_t value)
> +{
> +    return (bitrev8(value & 0xff) << 8) | bitrev8(value >> 8);
> +}
> +
> +/**
> + * bitrev32:
> + * @value: the value to reverse bit ordering from
> + *
> + * Reverse the 32 bit input @value
> + *
> + * Returns: the input @value with reversed bit ordering
> + */
> +static inline uint32_t bitrev32(uint32_t value)
> +{
> +    return (bitrev16(value & 0xffff) << 16) | bitrev16(value >> 16);
> +}
> +
> +/**
> + * bitrev64:
> + * @value: the value to reverse bit ordering from
> + *
> + * Reverse the 64 bit input @value
> + *
> + * Returns: the input @value with reversed bit ordering
> + */
> +static inline uint64_t bitrev64(uint64_t value)
> +{
> +    return ((uint64_t)bitrev32(value & 0xffffffffULL) << 32)
> +        | (uint64_t)bitrev32(value >> 32);
> +}
> +
>  #endif
>