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specification.md

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reqvm specification

reqvm is a register based bytecode VM.

Floating point won't be supported for a while.

reqvm has a 8MiB stack, however the operations work on 8-byte integers, as such you can store 1'048'576 values on it.

Binaries

Binaries start with a 256 byte preamble. I've no idea if I'll ever fill this up, but whatever.

Preamble format

Binaries will start with the following magic byte string !reqvm;VSszMEI2VSszMEVGVSszMEZDVSszMEVCVSszMEM5VSswMDIxVSs2NjQyVSszMDg4VSs2QjYyVSszMDdFVSszMDhDVSswMDIx\n.
Then a string of bytes following this format: !<major>;<minor>;<patch>;<enabled features>;. major, minor, and patch are 2-byte numbers. enabled features is a string of bytes, every byte represents an individual optional feature, and the presence of the byte enables it.
This is padded with noops until 256 bytes have been reached.

After that follows the program itself.

Registers

All registers will be 64bit. List of registers:

  • 64 general purpose registers: gp0..63
  • 16 integer function argument registers: ifa0..15
  • program counter(read only): pc
  • a register dedicated to the return value of the last function: ire
  • the stack pointer: sp(read only)

Internal VM flags

  • CF("comparison flag") - stores the result of a comparison between two registers. Possible values(these will be reffered to as cf::value): eq(equal), less(less than), gr(greater than).

Instruction table

opcode(byte) mnemonic instruction notes
00 noop noop is a noop
01 call call func_name calls the function func_name
02 ret ret returns from a function, performing necessary cleanup
10 io io op reg the io metainstruction expect a 1-byte argument after it called the op which represent the I/O operation to be performed. See I/O operations
20 add add r1, r2 adds r1 and r2, stores result in r1
21 sub sub r1, r2 subtract r2 from r1, stores result in r1
22 mul mul r1, r2 multiplies r1 by r2, stores result in r1
23 div div r1, r2 divides r1 by r2, stores quotient in r1
24 mod mod r1, r2 divides r1 by r2, stores remainder in r1
25 and and r1, r2 bitwise ANDs r1 and r2, stores result in r1
26 or or r1, r2 bitwise ORs r1 and r2, stores result in r1
27 xor xor r1, r2 bitwise XORs r1 and r2, stores result in r1
28 not not r1 bitwise NOTs r1, stores result in r1
29 lshft lshft r1, r2 Performs r1 <<= r2
30 rshft rshft r1, r2 Performs r1 >>= r2
35 push push reg pushes reg onto the stack, increases the sp by 1
36 pushc pushc constant pushes the constant on the stack, stored in the binary as 8 bytes
37 pop pop reg pops the top value from the stack into reg
42 cmp cmp r1, r2 compares r1 and r2, stores result in CF
43 jmp jmp label jumps to label
44 jeq jeq label if CF == cf::eq, jumps to label
45 jneq jneq label if CF != cf::eq jumps to label
46 jl jl label if CF == cf::less, jumps to label
47 jleq jleq label if CF == cf::less or CF == cf::eq, jumps to label
48 jg jg label if CF == cf::gr, jumps to label
49 jgeq jgeq label if CF == cf::gr or CF == cf::eq, jumps to label
255 halt halt stops program execution, and the VM, returning the value in ire to the OS

I/O Operations

byte mnemonic argument notes
01 getc a register gets a character from stdin and stores it in the register passed as argument
02 putc a register interprets the register given as argument as an 8-bit character and outputs it to stdout
03 put8c a register interprets the register as a string of 8 8-bit characters and outputs them to stdout
04 putn a register interprets the register as a 64-bit number and outputs it to stdout