Batch Calcs.. Not the same as usual - batch-file

Question

I'm trying to make a desktop binary calculator and can't seem to get values to calculate properly.
http://pastebin.com/embed_js.php?i=mtsJRys8
:: functions for 128
if userValue GEQ 128 (
set bin128 = 1
goto 64
)
if not userValue GEQ 128 (
set bin128 = 0
)
Trying to get the Variable 'bin128' to end with a value 1 or 0

Answer 1

Decimal to binary converter?
I see in your paste you're computing the binary result by comparing the entered number with powers of two. There's a more efficient algorithm for converting dec to bin, and it'll handle numbers from 0 to 2147483647.
#echo off
setlocal
if "%~1"=="" (
echo usage: %~nx0 integer
goto :EOF
)
set /a dec = %~1
:/2
set /a mod = dec %% 2, dec /= 2
set "bin=%mod%%bin%"
if %dec% gtr 0 goto :/2
echo %bin%
I also see paulsm4's comment recommending another (suspicious quote) "real" language. Truthfully, though, not counting languages that already have a direct int-to-bin conversion method, the batch scripting language can actually save you a few steps because all math is integer math, with decimals inherently truncated. This saves you from having to Math.floor or similar on every iteration. This is one situation where batch is better-suited for the task than many other languages.
If you prefer to do the power-of-two comparison method, here's another solution. It loops 31 times regardless of the length of the numeral you supply, but for /L is very efficient. This may actually be faster than the method above for larger numbers for many iterations. Not sure.
#echo off
setlocal enabledelayedexpansion
if "%~1"=="" (
echo usage: %~nx0 integer
goto :EOF
)
set /a dec = %~1, pow = 1073741824
for /L %%I in (1,1,31) do (
if !dec! geq !pow! (
set "bin=!bin!1"
set /a dec -= pow
) else (
if defined bin set "bin=!bin!0"
)
set /a pow /= 2
)
if not defined bin set bin=0
echo %bin%
And just because I felt like it, here's the same thing but using bitwise operations. This is the most efficient method. (Edit: or at least it was, until Aacini posted his solution.)
#echo off
setlocal enabledelayedexpansion
if "%~1"=="" (
echo usage: %~nx0 integer
goto :EOF
)
for /L %%I in (0,1,30) do (
set /a "mask = 1 << %%I, bit = ^!^!(%~1 & mask)"
if !mask! gtr %~1 goto break
set "bin=!bit!!bin!"
)
:break
if not defined bin set bin=0
echo %bin%
Efficiency:
I ran a series of tests to determine which method is most efficient. For each method, I sent the output to NUL, looped the script for 1000 iterations, then took an average of the run times over 3 runnings. I did this first with a small value of 5, then a large value of 2147483646. Results:
goto method, input=small: 7.37 seconds
goto method, input=large: 33.77 seconds
powers-of-two method, input=small: 8.38 seconds
powers-of-two method, input=large: 12.44 seconds
bitwise method, input=small: 6.35 seconds
bitwise method, input=large: 11.42 seconds
These results are not surprising, as for /L is generally faster than a goto loop, and bitwise operations occur faster than integer math.

Answer 2

Just to complete rojo's answer, I think that this is the most efficient method to convert a decimal number to binary:
#echo off
setlocal EnableDelayedExpansion
if "%~1"=="" (
echo usage: %~nx0 integer
goto :EOF
)
set "decimal=%~1"
set "binary="
for /L %%i in (1,1,32) do (
set /A "bit=decimal&1, decimal>>=1"
set "binary=!bit!!binary!"
if !decimal! equ 0 goto break
)
:break
echo %binary%
Note that previous method correctly convert negative numbers!
At this post there is a Batch file that can convert very large decimal numbers to binary. The result is stored in a Batch variable, so the binary number may have a maximum of 8 K digits. This means that the maximum decimal number that can be converted is 2^8192 - 1.