[Vm-dev] Imminent change to Spur image format

Bert Freudenberg bert at freudenbergs.de
Mon Aug 11 15:37:18 UTC 2014

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?

- Bert -

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