wraparound fixnum operations in the implementation of flbit-field
#963
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This change will have no affect on the machine code generated for `flbit-field`, normally, since `fx-` and `fx-/wraparound` produce the same code in unsafe mode, as do `fxsll` and `fxsll/wraparound`. But this repair avoids failure in "fl.ms" afer compiling Chez Scheme itself in safe mode with something like `zuo . o=0`. Another possibility is to allow only a smaller bit width (by 1 bit) to reach the relevant expression. Using wraparound operators seems more conservative in that it keeps the generated code the same.
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This change will have no affect on the machine code generated for
flbit-field, normally, sincefx-andfx-/wraparoundproduce the same code in unsafe mode, as dofxsllandfxsll/wraparound. But this repair avoids failure in "fl.ms" afer compiling Chez Scheme itself in safe mode with something likezuo . o=0.Another possibility is to allow only a smaller bit width (by 1 bit) to reach the relevant expression. Using wraparound operators seems more conservative in that it keeps the generated code the same.