Mitra VM v0.1

	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R
1	Mitra VM Architecture
2		Belt
3		Instead of a stack or registers, Mitra has a “belt” (like conveyor belt), which kinda combines the strengths of both. A belt is like a stack, but items are only ever pushed, never poped, and after they reach a certain height, items too deep are simply dropped. This has a couple of handy advantages.
4		Mitra can store up to 16 items on its belt. Instructions can reference any item on the belt, not just the top ones as with a stack based machine.
5		Say this is the current state of the belt:
6			0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
7			5	8	6	1	8	4	2	6	9	4	2	5	8	5	3	9
8
9			If we now execute the operation add(<3>, <13>), it will add 1+5, and drop the value from the belt:
10			0	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
11			6	5	8	6	1	8	4	2	6	9	4	2	5	8	5	3
12
13		Locals
14		Similar to WebAssembly, there are operations for putting values from the belt to “local variables”, which can be retrieved later.
15		It‘s only possible to put the top value of the belt into local variables.
16
17		Type System
18		There are 5 types for Mitra code:
19			i8	8-bit integer (signed or unsigned)
20			i16	16-bit integer (signed or unsigned)
21			i32	32-bit integer (signed or unsigned)
22			i64	64-bit integer (signed or unsigned)
23			i128	128-bit integer (signed or unsigned)
24			slice	Pair of 32-bit unsigned integers pointing to a slice of memory, either read-only or read-write.
25
26		All values on the belt and of local variables are typed. Operations return types values depend on what‘s currently on the belt.
27		Operations automatically promote values to the highest bit size of the operand.
28		So say we want to add 5 (i8) and 10 (i32), the then the i8 will be promoted to an i32, and then 32-bit addition is performed.
29		Operations specify if the smaller value should be 0- or sign-extended. If they don‘t, (like 'and'), they‘re 0-extended.
30		Types are inferable for all operations before execution.
31
32		NaN
33		Some operations can fail, like load, div, in which case they return a NaN. This value is only possible on the belt and for locals, but not for the memory.
34		Any operation that gets a NaN as input also returns NaN. Results can be verified, in which case they trap and fail the transaction if they are NaN.
35		Any store operation traps and fails the transaction if any of its parameters is a NaN.
36
37		Slices
38		Slices point to a range of memory (start & length). All slices are read-only except for the pre-allocated RAM for the execution.
39		No memory is ever allocated inside the Mitra VM.
40		Slices can be created by either shrinking/subslicing an existing slice or getting one from the data provided by the VM.
41		For example, the txinfo.input_bytecode_at opcode returns a read-only slice containing the bytecode of a specific input. This slice
42		can be shrinked/subsliced, but it cannot be written to.
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100