Farid Zaripov wrote:
-----Original Message-----
From: Martin Sebor [mailto:[EMAIL PROTECTED]
Sent: Monday, October 09, 2006 10:55 PM
To: [email protected]
Subject: Re: [PATCH] bitset.cc (STDCXX-297)
the bitset). Also, I think the code could be simplified as
follows:
nbytes = (((maxbits | (sizeof *bits * CHAR_BIT - 1)) >> 5)
+ (0 != (maxbits & (sizeof *bits * CHAR_BIT - 1)))) << 2;
With the magic 5 and 2 replaced by expressions parametrized
on sizeof *bits, of course.
How log2 can be calculated at compile time?
5 is log2(sizeof (*bits) * CHAR_BIT)
2 is log2(sizeof (*bits))
I suppose you could use some metaprogramming tricks but I wouldn't
recommend it for portability ;-)
template <unsigned N>
struct log2 {
static const unsigned long value =
1 < N ? 1 + log2<(N >> 1)>::value : 0;
};
template <>
struct log2<0> { static const unsigned long value = 0; };
I would just hardcode it based on the size of the type. Something
simple like this (the same code is at the top of bitset.cpp) will
work:
enum {
#if 4 == _RWSTD_ULONG_SIZE
log2_long_size = 2,
log2_long_bits = 5
#lif 8 == _RWSTD_ULONG_SIZE
log2_long_size = 3,
log2_long_bits = 6
#else
log2_long_size = 4,
log2_long_bits = 7
#endif
};
Martin
