3.07 beta needed bug fix

[Jason Martin]

Rexx is famous for its Math handling and this is a Math bug.

It may break someone's old code but that code is technically already broken.

[#NETREXX-145] HashCode() math using char[] with length > 14 all cells = max char

Description
if using max char if using max char
Pass hash * 7 (((int) (chars [i])) * 2)) ((int) (chars [(chars.length - i) - 1] )) hash exception
0 0 131072 65536 196608
1 1376256 131072 65536 1572864
2 11010048 131072 65536 11206656
3 78446592 131072 65536 78643200
4 550502400 131072 65536 550699008
5 3854893056 131072 65536 3855089664 Overflow
6 26985627648 131072 65536 26985824256 Overflow
int.max 2147483647

The fix is already in two branchs.

https://sourceforge.net/p/netrexx/code/ci/6ca99c887037559988181db9c77ce5256e768645/

https://sourceforge.net/p/netrexx/code/ci/2e668699db737ac733fc2742fcd700af839da5d4/

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[ThSITC]

Hello Jason,

I do find your mail quite interesting, but don't understand what has been the original problem/bug :-(

Time and Energy to explain, please ?

Thomas Schneider.

====================================================================================

Am 29.07.2018 um 15:42 schrieb Jason Martin:

Rexx is famous for its Math handling and this is a Math bug.

It may break someone's old code but that code is technically already broken.

[#NETREXX-145] HashCode() math using char[] with length > 14 all cells = max char

Description
if using max char if using max char
Pass hash * 7 (((int) (chars [i])) * 2)) ((int) (chars [(chars.length - i) - 1] )) hash exception
0 0 131072 65536 196608
1 1376256 131072 65536 1572864
2 11010048 131072 65536 11206656
3 78446592 131072 65536 78643200
4 550502400 131072 65536 550699008
5 3854893056 131072 65536 3855089664 Overflow
6 26985627648 131072 65536 26985824256 Overflow
int.max 2147483647

The fix is already in two branchs.

https://sourceforge.net/p/netrexx/code/ci/6ca99c887037559988181db9c77ce5256e768645/

https://sourceforge.net/p/netrexx/code/ci/2e668699db737ac733fc2742fcd700af839da5d4/

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[Jason Martin]

-- OLD FUNCTION in Rexx.nrx NetRexx 3.06 and lower
--
-- 01 /** Return a hashcode for the value.
-- 02 */
-- 03 method hashCode returns int
-- 04 if chars=null then chars=layout()
-- 05 if chars.length<14 then over=(chars.length+1)%2
-- 06            else over=7
-- 07 /* Hash the first and last OVER characters */
-- 08 hash=0
-- 09 loop i=0 to over-1
-- 10   hash=hash*7+int(chars[i])*2+int(chars[chars.length-i-1])
-- 11   end i
-- 12 return hash
--
MAX_LEGAL_JAVA_CHAR = Rexx char(Integer.MAX_VALUE)

TRIGGER_ELSE_IN_LINE_06_ABOVE = MAX_LEGAL_JAVA_CHAR.copies(15)

say TRIGGER_ELSE_IN_LINE_06_ABOVE.hashCode()

--Program overflow.nrx
--===== Exec: overflow =====
--1215608709

A sample as best I can remember problem, René commited the fix.

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[Jason Martin]

Sorry bad example.

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[Jason Martin]

MAX_LEGAL_JAVA_CHAR = Rexx char(Integer.MAX_VALUE)

TRIGGER_ELSE_IN_LINE_06_ABOVE = MAX_LEGAL_JAVA_CHAR.copies(15)

-- Maybe not bad example but let us look at line 10 above

-- Any char in the 15 copies will have a value of 65535

-- So int(chars[i]) will always be 65535

-- So int(chars[chars.length-i-1]) will always be 65535

hash=0

loop i=0 to 6
   hash=hash*7+65535*2+65535
   say "loop # :" i
   say "hash math :" hash
   -- say "TRY THIS hash math :" hash.toint()
end

say "IS YOUR HASH ONE OF THE #'s ABOVE? :"
TRIGGER_ELSE_IN_LINE_06_ABOVE.hashCode()


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[ThSITC]

Hello Jason, I don't yet understand *fully*, but *thanks for the answer* :-)

Thomas Schneider.

==================================================================

Am 31.07.2018 um 05:57 schrieb Jason Martin:

-- OLD FUNCTION in Rexx.nrx NetRexx 3.06 and lower
--
-- 01 /** Return a hashcode for the value.
-- 02 */
-- 03 method hashCode returns int
-- 04 if chars=null then chars=layout()
-- 05 if chars.length<14 then over=(chars.length+1)%2
-- 06            else over=7
-- 07 /* Hash the first and last OVER characters */
-- 08 hash=0
-- 09 loop i=0 to over-1
-- 10   hash=hash*7+int(chars[i])*2+int(chars[chars.length-i-1])
-- 11   end i
-- 12 return hash
--
MAX_LEGAL_JAVA_CHAR = Rexx char(Integer.MAX_VALUE)

TRIGGER_ELSE_IN_LINE_06_ABOVE = MAX_LEGAL_JAVA_CHAR.copies(15)

say TRIGGER_ELSE_IN_LINE_06_ABOVE.hashCode()

--Program overflow.nrx
--===== Exec: overflow =====
--1215608709

A sample as best I can remember problem, René commited the fix.

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[Jason Martin]

-- I can think a little better today.
-- Copy all this and save and nrc -exec saved
-- Then uncomment -- say "UNCOMMENT to see OVERFLOW :" hash.toint()
-- Run again.

MAX_LEGAL_JAVA_CHAR = Rexx char(Character.MAX_VALUE)

say "int value of MAX_LEGAL_JAVA_CHAR : " MAX_LEGAL_JAVA_CHAR.c2d()

-- Maybe not bad example but let us look at the MATH
--   "hash=hash*7+int(chars[i])*2+int(chars[chars.length-i-1])"

A_REXX_WITH_15_JAVA_MAX_CHARS = MAX_LEGAL_JAVA_CHAR.copies(15)

-- Any of the 15 chars have a int value of 65535

-- So int(chars[i]) will always be 65535

-- So int(chars[chars.length-i-1]) will always be 65535

-- BEGIN SIMPLE LOOP MATH

hash=0

loop i=0 to 6
   hash=hash*7+65535*2+65535
   say "loop # :" i
   say "hash math :" hash
   -- say "UNCOMMENT to see OVERFLOW :" hash.toint()
end

-- END SIMPLE LOOP MATH

say "WAS THE HASH RETURNED, ONE FROM THE LOOP MATH ABOVE? :"
A_REXX_WITH_15_JAVA_MAX_CHARS.hashCode()


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