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Note that if you are using 32-bit addressing, as will be the case by default (see 32-bit addressing, you should use ordinary long integer arithmetic and should not use UADD and USUB.
However if you have used SETFLAGS to enforce the 64K memory limit, whenever you wish to add or subtract something from an integer which is an address of something (or a pointer to something) you should use UADD and USUB. If you do not, you will risk an ‘Integer overflow’ error.
An integer address can be any value from 0 to 65535. An integer variable can hold the full range of addresses, but treats those values from 32768 to 65535 as if they were -32768 to -1. If your addition or subtraction would convert an address in the 0-32767 range to one in the 32768-65535 range, or vice versa, this would cause an ‘Integer overflow’.
UADD and USUB treat integers as if they were unsigned, i.e. as if they really held a value from 0 to 65535.
For example, to add 1 to the address of a text string (in order to skip over its leading byte count and point to the first character in the string), use i%=UADD(ADDR(a$),1), not i%=ADDR(a$)+1.
USUB works in a similar way, subtracting the second integer value from the first integer, in unsigned fashion for example, USUB(ADDR(c%),3).
USUB(x%,y%) has the same effect as UADD(x%,-y%).
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