bcpl64: constant folding does not work for 64 bit expressions

[dgottner]

I've used BCPL for many 64 bit Project Euler problems, but I've noticed an issue when compile-time expressions exceed 32 bits; the results are incorrect. Here is an example:

GET "libhdr"

LET start() = VALOF {
    LET x = ?
    x := 999 * 10_000_000
    writef("x = %d *n", x)
    x := 999
    x *:= 10_000_000
    writef("x = %d *n", x)
    RESULTIS 0
}

Using bcpl64 compile, the output is:

x = 14284967296
x = 9990000000

The first result, where the compiler did constant folding is wrong. The second result, where the the calculation was done at runtime is correct.