On Tuesday, 6 September 2011 00:51:54 UTC+10, Joep wrote:
>
> > rather than:
> > y = y & 63 -- or equivalent constant
>
> Check with y=180 (not sure if it is an intended difference though).
>
Is that a trick question? I don't think they are different.
I got all unit-testy, the following Ruby script (which runs all the Jal
if/thens unmodified*) says they produce the same value for all 8-bit
numbers:
#! /usr/bin/ruby
SCREEN_MAX_Y = 63
SCREEN_ROWS = 64
def three_ifs_way(y)
if y > 191 then
y = y - 192
elsif y > 127 then
y = y - 128
elsif y > SCREEN_MAX_Y then
y = y - SCREEN_ROWS
end
return y
end
def one_AND_way(y)
return y & 63
end
#### main loop
return_value = 0
for i in 0..255
if three_ifs_way(i) != one_AND_way(i) then
puts "Bad! Methods differ for value #{i}"
return_value += 1
end
end
exit return_value
* had to change "end if" to just "end"
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