&H8000 to &HFFFF Hex = -32,768 to -1, Affects LONG Bit Masking

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SUMMARY
This article concerns assigning a LONG integer to a hexadecimalconstant in the range &H8000 through &HFFFF hex. This information isespecially important if you intend to do any bit manipulation with thelogical operators (AND, OR, NOT, XOR, EQV, or IMP) with any LONGinteger larger than &HFFFF& hex (or 65,535 decimal) that has at leastone bit from 16 through 32 on.

Many programmers may not realize that the constants &H8000 through&HFFFF default to a type of short integer, representing decimal values-32,768% through -1% respectively. Also note that the LONG-integerconstants &H8000& through &HFFFF& represent decimal values +32,768 to+65,535. Basic must follow these integer-type notation standards andbehaviors since it doesn't have an unsigned data type.

This information applies to Microsoft QuickBasic versions 4.00, 4.00b,and 4.50, to Microsoft Basic Compiler versions 6.00 and 6.00b forMS-DOS and MS OS/2, and to Microsoft Basic Professional DevelopmentSystem (PDS) versions 7.00 and 7.10 for MS-DOS and MS OS/2.
MORE INFORMATION
Assigning a LONG integer variable to a short integer hexadecimalconstant in the range &H8000 through &HFFFF adds &HFFFF0000 to thenumber, resulting in the LONG integer being stored as &HFFFF8000 to&HFFFFFFFF (that is, -32,768& to -1& decimal).

This behavior occurs because constants &H8000 through &HFFFF defaultto a type of short integer (%). In short integer notation, constants&H8000 through &HFFFF have decimal values -32,768% through -1%,respectively. For example:
   PRINT VAL("&HFFFF"); &HFFFF   ' Prints:  -1 -1   PRINT VAL("&H8000"); &H8000   ' Prints:  -32768 -32768				
To assign hex constants &H8000 through &HFFFF to a LONG integerwithout turning on bits 16 through 32 (&HFFFF0000), you must changethem to a type of LONG by appending an ampersand (&) character asfollows:
   LongInt& = &H8000&  ' Use &H8000& (or +32768) instead of &H8000   LongInt& = &H8001&  ' Use &H8001& (or +32769) instead of &H8001      . . .                . . .   LongInt& = &HFFFF&  ' Use &HFFFF& (or +65535) instead of &HFFFF				
Appending "&" to the constant is not necessary for hex constantsoutside the range &H8000& through &HFFFF&.

The LONG integer &HFFFF& hex is equal to 65,535 decimal. The shortinteger &HFFFF hex is equal to -1 decimal (according to the signed,two's complement, integer format standard). A -1 in decimal notationis &HFFFFFFFF in hex LONG-integer notation.

The hexadecimal constants &H8000 through &HFFFF default to shortintegers &H8000% through &HFFFF%, which represent the decimal numbers-32,768% to -1% in the two's complement, signed binary integer format.You must append an ampersand (&) character to the end of the constantto make it a LONG integer, as follows: &H8000& through &HFFFF& (whichrepresent the decimal numbers 32,768 through 65,535).

The hexadecimal constants &HFFFF8000 to &HFFFFFFFF are LONG integersthat represent the decimal numbers -32,768& to -1& in the two'scomplement, signed binary integer format.

Note: Bit masking (manipulation) is normally NOT done withfloating-point numbers, because of the nature of the floating-pointformat. Bit masking normally is useful only with integers.

Code Example 1

'a& is a variable, and b& will serve as a bit mask:a& = &HFFFF0000 ' &HFFFF0000 is a constant of type LONGb& = &HFFFF&  ' ATTENTION: Assign &HFFFF& instead of &HFFFF'This masks out bits 16 through 32, and keeps bits 1 through 15:a& = a& AND b&PRINT "a& AND b& = "; a&, HEX$(a&); " prints zero (all bits off)"' Assigning b& to &HFFFF instead of &HFFFF& changes the result:b& = &HFFFF' Now, b& contains &HFFFFFFFF, or -1 (all bits on). ANDing with b&' does not change a&:a& = a& AND b&PRINT "a& AND b& = "; a&, HEX$(a&); " prints -65536, hex FFFF0000"				

Code Example 2

' The following assigns short constant &HFFFF (-1) to a LONG' integer. &HFFFF is converted to &HFFFFFFFF; the decimal' value (-1) stays the same:longint& = &HFFFFshortint% = &HFFFFPRINT "longint& =", longint&, HEX$(longint&)PRINT "shortint% =", shortint%, HEX$(shortint%)' The following assigns short constant &H8000 (-32,768) to a LONG' integer. &H8000 is converted to &HFFFF8000; the decimal' value (-32,768) stays the same:longint& = &H8000shortint% = &H8000PRINT "longint& =", longint&, HEX$(longint&)PRINT "shortint% =", shortint%, HEX$(shortint%)				
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Article ID: 38888 - Last Review: 02/27/2014 20:59:16 - Revision: 1.2

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