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I was originally thinking of making a lookup table, but thought of this along the way.

Thanks for that - I still haven't worked my way through it properly.
It seems to work fine now that I've changed:
long long smallest_invalid = last_set << 52; to long long smallest_invalid = last_set << 53;
Without that change, the following values (for example) wrongly reported "NOPE":
1844674407366955264, 1844674407366955776, 1844674407366956288, 1844674407366956800, 1844674407366957312, 1844674407366957824, 1844674407366958336, 1844674407366958848, 1844674407366959360, 1844674407366959872, 1844674407366960384, 1844674407366960896, 1844674407366961408, 1844674407366961920, 1844674407366962432, 1844674407366962944, 1844674407366963456, 1844674407366963968, 1844674407366964480, 1844674407366964992
In the following XS adaptation it's taking over twice as long as uv_fits_double3.
use warnings; use Benchmark; use Inline C => Config => BUILD_NOISY => 1; use Inline C => <<'EOC'; int uv_fits_double3(SV * x, ...) { dXSARGS; int i, count = 0; UV arg; for(i = 0; i < items; i++) { arg = SvUV(ST(i)); if(arg) { while(!(arg & 1)) arg >>= 1; if(arg < 9007199254740993) count++; } } return count; } int uv_fits_double_bitfiddle(SV * t, ...) { dXSARGS; int i, count = 0; for(i = 0; i < items; i++) { /* First we need to identify the lowest bit set */ IV neg_t = -(SvIV(ST(i))); IV last_set = SvUV(ST(i)) & neg_t; /* Shift it left 53 bits to get location of lowest invalid bit + * * NOTE: If smallest invalid bit is far enough left, then this wil +l * * turn into 0 making the invalid bits also 0, which happens to be + OK! */ IV smallest_invalid = last_set << 53; UV valid_bits = smallest_invalid - 1; UV invalid_bits = ~valid_bits; /* It's a 'valid' number unless one of the upper-order invalid bit +s are set */ if(!(SvUV(ST(i)) & invalid_bits)) count++; } return count; } EOC @in = (1844674407366955161 .. 1844674407378955161); # @in = (9007199248740992 .. 9007199260740992); # @in = (184467436737095 .. 184467448737095); # @in = (184463440737 .. 184475440737); die "wrong size" unless @in == 12000001; timethese (1, { 'uv_fits_double3' => '$count1 = uv_fits_double3(@in);', 'uv_fits_double_bitfiddle' => '$count2 = uv_fits_double_bitfiddle(@in) +;', }); print "$count1 $count2\n"; die "Error in at least one of the XSubs" unless $count1 == $count2; __END__
Benchmarking results on my Windows 7 machine with perl-5.30.0 are:
Benchmark: timing 1 iterations of uv_fits_double3, uv_fits_double_bitf +iddle... uv_fits_double3: 0 wallclock secs ( 0.44 usr + 0.00 sys = 0.44 CPU) + @ 2.29/s (n=1) (warning: too few iterations for a reliable count) uv_fits_double_bitfiddle: 1 wallclock secs ( 0.94 usr + 0.00 sys = +0.94 CPU) @ 1.07/s (n=1) (warning: too few iterations for a reliable count) 12000001 12000001
Can you see room for significant improvement in performance of uv_fits_double_bitfiddle ?

Thanks for another interesting approach !!

Cheers,
Rob

In reply to Re^2: Detecting whether UV fits into an NV by syphilis
in thread Detecting whether UV fits into an NV by syphilis

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