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Default C just lets overflows occur for subtraction, so this macro
will default to 0 if the subtraction causes an overflow.
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Just prints instructions so far.
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Though we deal with unsigned numbers internally, it should be possible
to read and manipulate negative numbers through 2s complement. Later
on we'll add support for signed operations via 2s complement, so this
should be allowed.
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This is an easy fix.
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Doesn't make sense for them to be in the VM module when they have a
more general purpose now.
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Also prints a usage for incorrect usage.
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No implementations yet
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Pretty simple tokeniser, doesn't do a lot and needs to error check better.
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If an empty file is read, we want to deal with it in later user code
rather than just failing immediately.
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Easier to write includes now just using < with the module name, in
comparison to using relative paths.
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Changed folder names for sake of clarity (will be introducing a new
build target soon), and Makefile can now easily support more targets.
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Performs a jump when the (BYTE|HWORD|WORD) at the top of the stack is
non zero.
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Checks if the operand given is a well defined program address, then
performs the jump.
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This is because we just OR the bits into the specific byte of the
word. This means the previous state may leave artefacts as the OR
doesn't clear the bits away.
To do so, we apply a bit mask to clear the specified byte(s) of the
word, then perform the OR.
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First the program, then the registers then the stack.
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Prints an error message, returns a non zero code based on error
code (255 - err).
In main, I propagate this exit code.
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This is simply a program with an embedded set of instructions which
indefinitely computes and prints fibonacci numbers, computing them in
pairs.
Does it completely through the virtual machine rather than just hard C
instructions.
Also amended the Makefile to compile it. Required moving the main.c
object file into the dependencies of $(DIST)/$(OUT).
I should track the dependencies for fib.c and main.c as well.
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Also fixed an overflow error in vm_dup_word, where I underflow the
index of vm->stack.data which causes a buffer overflow.
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Here is where we may have differing interpretations of what the bits
in the data pile may actually mean. This in particular refers to
printing the signed or unsigned versions of the bits given. Also,
interpreting some byte as a character or just a raw number.
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Only happens when vm_print_program(STDERR), as STDERR occurs before
STDOUT on Emacs. So while the lines would print, no instructions
would follow. This fixes that by using fp.
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Was only used for OP_PUSH data types anyway, so is essentially
useless. Only OP_PUSH has operands after it that directly relate to
it: the rest either have a fixed type (a byte for registers, for
example) or NIL (because they have no operand).
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Routines that use the stack for their operands i.e. aren't supplied
operands directly all have the same signature. We may as well stick
them all together in one array and one conditional, just reduces the
number of branches. Also looks nicer.
Implemented OP_PLUS_*. Pretty simple to implement.
Deleted vm_peek as it was only necessary to update the `ret` register.
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Takes two operands from the stack then pushes their sum.
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Every vm routine now returns an err_t, which is an enumeration of
possible error states. ERR_OK represents the good state and is 0 so
error checking seems very natural in terms of language `if (err) ...`.
Errors bubble up the runtime, with any callers forced to check if an
error occurred.
This does mean that routines that call other routines cannot provide
an accurate trace of the subcaller (based on the fact that an error is
generated for the current instruction), but this should be a non issue
as no instruction should be complex enough to need proper traces.
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Uses the stack and register, respectively, to jump to an absolute
address. The stack based jump pops a word off the stack to perform a
jump, while the register based one uses the operand to figure out
which register to use.
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Wasn't useful or necessary.
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Jumps to the operand given, interpreted as a word, an absolute
address.
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This adds a bound on vm_execute_all to stop program->ptr from going
past program->max.
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Wasn't very secure for endianness, and using these helpers abstracts
the details away a bit in case I want to enforce a certain system.
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If I add a new operand I want the build system to be more helpful in
finding the places I need to change to make it work.
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Duplicates the nth datum off the stack, pushing it to the top. Useful
for operations such as MOV which eat the stack.
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Use (H)WORD_SIZE more, added some notes, etc
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Uses memcpy internally, so we don't need to care about endianness.
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