[Vm-dev] Imminent change to Spur image format

Clément Bera bera.clement at gmail.com
Mon Aug 11 16:16:39 UTC 2014

2014-08-11 17:37 GMT+02:00 Bert Freudenberg <bert at freudenbergs.de>:

> On 09.08.2014, at 00:46, Eliot Miranda <eliot.miranda at gmail.com> wrote:
> > Hi All,
> >
> >     as part of the Newspeak infrastructure we use at Cadence I
> implemented multiple bytecode set support and a lifting of the limits in a
> method on the number of literals and the span of branches about two years
> ago.  This work involved adding a second interpretation to the bits in a
> method header, providing 16 bits of literal count.  This was done by moving
> the primitive number out of the method header and into an optional
> callPrimitive bytecode, being the first bytecode of methods that have
> primitives.
> >
> > Now in Spur I have the opportunity to use this expanded format for the
> exsting bytecode set as well.  The SqueakV3 set does not use bytecode 139,
> which is convenient to use for its callPrimitiveBytecode.  The advantage is
> that when and if a new bytecode set is added, as is planned for the Sista
> VMs, the VM will not have to test method headers to decide which format
> they're in, because there will only be one.
> Just curious: how does the VM know which bytecode set to use for a given
> method?
> A bit is set or not in the compiled method header.

> - Bert -
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