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Difference between revisions of "SCUMM/Virtual Machine"
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== The SCUMM virtual machine == | == The SCUMM virtual machine == | ||
The SCUMM virtual machine was given a complete rewrite between version 5 and version 6. Both virtual machines are simple byte-code machines with built-in cooperative threading; up to 25 threads can be run simultaneously. Each thread gets 16 words of local storage. Up to 8192 words and 32768 bits of global storage are also available. The word and bit storage areas occupy | The SCUMM virtual machine was given a complete rewrite between version 5 and version 6. Both virtual machines are simple byte-code machines with built-in cooperative threading; up to 25 threads can be run simultaneously. Each thread gets 16 words of local storage. Up to 8192 words and 32768 bits of global storage are also available. The word and bit storage areas occupy separate address spaces. The exception to this rule is Zak256, where both actually use the same memory (possibly this is also true for other older SCUMM versions). | ||
The V5 machine has hard-coded limits on 800 word variables and 2048 bit variables. All operations are done to and from a variable (global or local). The V6 machine can stores the number of variables in the '''MAXS''' resource in the index and uses a 100-word global stack for performing operations. | The V5 machine has hard-coded limits on 800 word variables and 2048 bit variables. All operations are done to and from a variable (global or local). The V6 machine can stores the number of variables in the '''MAXS''' resource in the index and uses a 100-word global stack for performing operations. | ||
Additional storage is supplied in Array resources. V5 requires arrays to be declared in the data file; V6 can define new ones on the fly, which means they can be used as a dynamic heap. | Additional storage is supplied in Array resources. V5 requires arrays to be declared in the data file; V6 can define new ones on the fly, which means they can be used as a dynamic heap. | ||
== Pointers == | == Pointers == | ||
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{| border="1" cellpadding="2" width=25% | {| border="1" cellpadding="2" width=25% | ||
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|15||14||13||12 ... 0 | |15||14||13||12 ... 0 | ||
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|0||0||0||address | |0||0||0||address | ||
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{| border="1" cellpadding="2" width=15% | {| border="1" cellpadding="2" width=15% | ||
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|1||address | |1||address | ||
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{| border="1" cellpadding="2" width=30% | {| border="1" cellpadding="2" width=30% | ||
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|0||1||?||0||var no | |0||1||?||0||var no | ||
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{| border="1" cellpadding="2" width=25% | {| border="1" cellpadding="2" width=25% | ||
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|0||0||1||address | |0||0||1||address | ||
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|0||0||I||offset | |0||0||I||offset | ||
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{| border="1" cellpadding="2" width=100% | {| border="1" cellpadding="2" width=100% | ||
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|State||Meaning | |State||Meaning | ||
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{| border="1" cellpadding="2" width=10% | {| border="1" cellpadding="2" width=10% | ||
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|7||6 ... 0 | |||
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|p1||$5A | |p1||$5A | ||
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