On 15/12/11 19:33, Bram Moolenaar wrote:
Ben Fritz wrote:
On Dec 14, 8:33 am, Bram Moolenaar<[email protected]> wrote:
Patch 7.3.377
Problem: No support for bitwise AND, OR, XOR and invert.
Solution: Add add(), or(), invert() and xor() functions.
Files: src/eval.c, src/testdir/test49.in, src/testdir/test65.in,
src/testdir/test65.ok, runtime/doc/eval.txt
A couple of things:
1. I note that the new functions are missing from :help function-list
(probably they should be under a new subheading, like "integer
computation" or "bitwise computation" similar to "floating point
computation").
Indeed, I'll add them there.
2. I note that no shift operators were defined. So now the easiest way
to do the shifting if needed is by multiplying or dividing by powers
of 2. But I just realized pow() is a floating-point function, making a
shift much more expensive than it needs to be, if this function is
used. I could not find a good way to get arbitrary (integer) powers of
2 with Vim functions/syntax. Can we either add the shift operators, or
add the ability to do integer exponentiation?
I haven't decided yet. In most cases you can simple do var * 2 or
var / 2. Only for very big numbers that may not work right.
If you really need to shift by something that is not a constant then
indeed it is more complicated.
The following should be fast enough but I haven't tested it. It can all
go in the vimrc or in a global plugin.
" Initialization. This implicitly takes sizeof(int) into account.
let PowersOfTwo = []
let n = 1
while n " n==0 means no error on overflow
try
let PowersOfTwo += [n]
let n += n
catch " if error on overflow
break
endtry
endwhile
" Auxiliary functions
func Pow2(x)
try
return PowersOfTwo[a:x]
catch
return -1
endtry
endfunc
func LeftShift(value, shift)
if a:shift < 0
return RightShift(a:value, - a:shift)
endif
try
let l:cpo = &cpo
set cpo&vim " recognise continuation lines
let s = Pow2(a:shift)
if s != -1
return a:value * s
endif
" errors are intentionally not caught
throw "Invalid arguments: LeftShift(" . a:value . ", "
\ . a:shift . ")"
finally
let &cpo = l:cpo
endtry
endfunc
func RightShift(value, shift)
if a:shift < 0
return LeftShift(a:value, - a:shift)
endif
try
let l:cpo = &cpo
set cpo&vim
let s = Pow2(a:shift)
if s != -1
return a:value / s
endif
throw "Invalid arguments: RightShift(" . a:value . ", "
\ . a:shift . ")"
finally
let &cpo = l:cpo
endtry
endfunc
Best regards,
Tony.
--
"People think love is an emotion. Love is good sense."
-- Ken Kesey
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