Bitwise Operations

Bitwise operations are used to perform an action on the bits (the 1's and 0's) of a number.

In this article a "binary" formatted number (which represents the "bits" of a number) will be written with a ²... and a decimal number with a ¹⁰

Limitations

In Sphere, numbers are stored in something called a "DWORD". The largest number a DWORD can store is constrained by the fact that a DWORD is 32 bits wide. That means the largest number it can store is 2^32-1.

• In Binary that's 11111111111111111111111111111111.
• In Hex it's FFFFFFFF.
• In Decimal that's 4294967295.

To store a 'signed' number in a DWORD (in other words, a number that can be positive or negative), the first bit is used to indicate the sign (a 1 is negative). Which means the largest 'signed' positive number is 2^31-1

• In Binary that's 01111111111111111111111111111111.
• In Hex it's 7FFFFFFF.
• In Decimal that's 2147483647.

In sphere script language, the EVAL function outputs a signed DWORD, and the UVAL outputs an unsigned DWORD.

[FUNCTION Mathtest]
LOCAL.Number0=2147483647
LOCAL.Number1=4294967295
LOCAL.Number2=8589934588
SERV.LOG eval0=<EVAL <LOCAL.Number0>> eval1=<EVAL <LOCAL.Number1>> eval2=<EVAL <LOCAL.Number2>>
SERV.LOG uval0=<UVAL <LOCAL.Number0>> uval1=<UVAL <LOCAL.Number1>> uval2=<UVAL <LOCAL.Number2>>

The output of this test is:

13:37:(test.scp,10)eval0=2147483647 eval1=-1 eval2=-4
13:37:(test.scp,11)uval0=2147483647 uval1=4294967295 uval2=4294967292

Notes:

• The output is limited to align with the limitation of the DWORD itself.
• Since there are 32 "bits" in a DWORD, there can only be 32 flags in a set.
• Be careful when manipulating flags using EVAL, because the 32nd flag could get lost.

Flags

In the Sphere server, quite a few concepts are implemented using "flags". You can see examples of flags being defined in the Sphere.ini file, or the sphere_defs.scp files. For example:

[DEFNAME attr_flags]
attr_identified       01
attr_decay            02
attr_newbie           04
attr_move_always      08
attr_move_never      010
attr_magic           020
attr_owned           040
attr_invis           080
attr_cursed         0100
attr_cursed2        0200
attr_blessed        0400
attr_blessed2       0800
attr_forsale       01000
attr_stolen        02000
attr_can_decay     04000
attr_static        08000
attr_exceptional  010000
attr_enchanted    020000
attr_imbued       040000
attr_questitem    080000
attr_insured     0100000
attr_nodrop      0200000
attr_notrade     0400000
attr_lockeddown  0800000
attr_secure     01000000

Notice a pattern? Let's tip it on it's side and chart the first 8 flags:

Flag Name:	attr_invis	attr_owned	attr_magic	attr_move_never	attr_move_always	attr_newbie	attr_decay	attr_identified
Binary Number:	10000000	01000000	00100000	00010000	00001000	00000100	00000010	00000001
Hex Number:	080	040	020	010	08	04	02	01
Decimal Number:	128	64	32	16	8	4	2	1