Re: [Qemu-devel] [PATCH v2] bitops.h: Add field32() and field64() functions to extract bitfields

[Avi Kivity]

On 06/27/2012 04:22 PM, Peter Maydell wrote:
> On 27 June 2012 14:15, Avi Kivity <address@hidden> wrote:
>> I suggest adding the analogous functions for writing.  I believe the
>> common naming is extract/deposit.
>>
>> static inline uint64_t deposit64(uint64_t *pvalue, unsigned start,
>>                                 unsigned length, uint64_t fieldval)
>> {
>>    uint64_t mask = (((uint64_t)1 << length) - 1) << start;
>>    *pvalue = (*pvalue & ~mask) | ((fieldval << start) & mask);
>> }
>>
>> Useful for setting a bit to a specific value.
> 
> Do you have a use case in mind for this one?

A fast grep:

hw/alpha_typhoon.c-    if (level) {
hw/alpha_typhoon.c:        drir |= 1ull << irq;
hw/alpha_typhoon.c-    } else {
hw/alpha_typhoon.c:        drir &= ~(1ull << irq);
hw/alpha_typhoon.c-    }

hw/cbus.c-    if (state)
hw/cbus.c:        s->status &= ~(1 << 5);
hw/cbus.c-    else
hw/cbus.c:        s->status |= 1 << 5;

hw/dma.c-    case 0x09:
hw/dma.c-        ichan = data & 3;
hw/dma.c-        if (data & 4) {
hw/dma.c:            d->status |= 1 << (ichan + 4);
hw/dma.c-        }
hw/dma.c-        else {
hw/dma.c:            d->status &= ~(1 << (ichan + 4));
hw/dma.c-        }
hw/dma.c:        d->status &= ~(1 << ichan);
hw/dma.c-        DMA_run();
hw/dma.c-        break;
hw/dma.c-
hw/dma.c-    case 0x0a:                  /* single mask */
hw/dma.c-        if (data & 4)
hw/dma.c:            d->mask |= 1 << (data & 3);
hw/dma.c-        else
hw/dma.c:            d->mask &= ~(1 << (data & 3));
hw/dma.c-        DMA_run();

hw/exynos4210_combiner.c-    if (level) {
hw/exynos4210_combiner.c:        s->group[group_n].src_pending |= 1 << bit_n;
hw/exynos4210_combiner.c-    } else {
hw/exynos4210_combiner.c:        s->group[group_n].src_pending &= ~(1 << bit_n);
hw/exynos4210_combiner.c-    }
hw/exynos4210_combiner.c-

I stopped here, but I'm sure there are plenty others.  Bitfields are common in 
hardware.

-- 
error compiling committee.c: too many arguments to function