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bug#22689: [PATCH] Add logcount
From: |
Eli Zaretskii |
Subject: |
bug#22689: [PATCH] Add logcount |
Date: |
Sat, 30 Sep 2017 14:42:51 +0300 |
> Date: Fri, 29 Sep 2017 13:41:34 -0400
> From: Mark Oteiza <mvoteiza@udel.edu>
>
> I made an attempt implementing this:
Thanks. I'm not an expert on these ops, but otherwise the code looks
OK to me, modulo the minor comments below.
This will eventually need a NEWS entry and some docs in the ELisp
manual.
> +#if defined (__POPCNT__) && defined (__GNUC__) && (__GNUC__> 4 ||
> (__GNUC__== 4 && __GNUC_MINOR__> 1))
> +#define HAVE_BUILTIN_POPCOUNTLL
> +#endif
Where does __POPCNT__ definition come from? I don't see it in my
GCC's "gcc -dM" output.
As for the rest of the condition, I think you should use GNUC_PREREQ,
like this:
#if GNUC_PREREQ (4, 1, 0)
> +static uint64_t
> +bitcount64 (uint64_t b)
> +{
> + b -= (b >> 1) & 0x5555555555555555;
> + b = (b & 0x3333333333333333) + ((b >> 2) & 0x3333333333333333);
> + b = (b + (b >> 4)) & 0x0f0f0f0f0f0f0f0f;
> + return (b * 0x0101010101010101) >> 56;
Shouldn't these constants have a ULL suffix, to make sure they are not
truncated to a 32-bit int?
> +#else /* HAVE_BUILTIN_POPCOUNTLL */
> + if (XINT (value) <= UINT_MAX)
> + XSETINT (res, bitcount32 (XUINT (value)));
> + else if (XINT (value) <= ULONG_MAX)
> + XSETINT (res, bitcount64 (XUINT (value)));
The comparisons against Uxxx_MAX seem to assume that VALUE is
unsigned, but that's not guaranteed, right?
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/29
- bug#22689: [PATCH] Add logcount,
Eli Zaretskii <=
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/30
- bug#22689: [PATCH] Add logcount, Eli Zaretskii, 2017/09/30
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/30
- bug#22689: [PATCH] Add logcount, Eli Zaretskii, 2017/09/30
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/30
- bug#22689: [PATCH] Add logcount, Eli Zaretskii, 2017/09/30
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/30
- bug#22689: [PATCH] Add logcount, Eli Zaretskii, 2017/09/30
- bug#22689: [PATCH] Add logcount, Mark Oteiza, 2017/09/30
- bug#22689: [PATCH] Add logcount, Benjamin Riefenstahl, 2017/09/30