On 01/09/2017 08:10 PM, Jose Ricardo Ziviani wrote: > Implements 128-bit left shift and right shift as well as their > testcases. By design, shift silently mods by 128, so the caller is > responsible to assert the shift range if necessary. > > Left shift sets the overflow flag if any non-zero digit is shifted out. > > Examples: > ulshift(&low, &high, 250, &overflow); > equivalent: n << 122 > > urshift(&low, &high, -2); > equivalent: n << 126 > > Signed-off-by: Jose Ricardo Ziviani <[email protected]> > ---
> +typedef struct {
> + uint64_t low;
> + uint64_t high;
> + uint64_t rlow;
> + uint64_t rhigh;
> + int32_t shift;
> + bool overflow;
> +} test_data;
> +
> +static const test_data test_ltable[] = {
> + { 0x4C7ULL, 0x0ULL, 0x00000000000004C7ULL,
> + 0x0000000000000000ULL, 0, false },
I might have laid it out as:
{ 0x00000000000004c7ULL, 0x0000000000000000ULL,
0x00000000000004c7ULL, 0x0000000000000000ULL,
0, false }
to make the pre- and post-shift values line up better. It's not fatal
to the patch, so it's up to the maintainer if they want a v6 to improve
the alignment.
> + { 0x8888888888888888ULL, 0x9999999999999999ULL,
> + 0x8000000000000000ULL, 0x9888888888888888ULL, 60, true },
> + { 0x8888888888888888ULL, 0x9999999999999999ULL,
> + 0x0000000000000000ULL, 0x8888888888888888ULL, 64, true },
These two are the most legible.
> +};
> +
> +static const test_data test_rtable[] = {
> +++ b/util/host-utils.c
> @@ -161,3 +161,67 @@ int divs128(int64_t *plow, int64_t *phigh, int64_t
> divisor)
> }
> #endif
>
> +/**
> + * urshift - 128-bit Unsigned Right Shift.
> + * @plow: in/out - lower 64-bit integer.
> + * @phigh: in/out - higher 64-bit integer.
> + * @shift: in - bytes to shift, between 0 and 127.
> + *
> + * Result is zero-extended and stored in plow/phigh, which are
> + * input/output variables. Shift values outside the range will
> + * be mod to 128. In other words, the caller is responsible to
> + * verify/assert both the shift range and plow/phigh pointers.
> + */
Duplicating docs in the .h and .c doesn't hurt, but risks one getting
out of date; we have other spots that put the docs in the .h (where
callers will look up what's available) or the .c (where the
implementation is there to check against the docs). I don't have any
strong preference on how to do it, though, so I don't mind leaving it as is.
Reviewed-by: Eric Blake <[email protected]>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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