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use ; comments to fix github highlighting

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Connor Olding 2016-01-24 20:18:52 -08:00
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38
README.md
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@ -52,49 +52,51 @@ It takes a couple notes from more traditional assemblers as well.
[caje]: https://github.com/Tarek701/CajeASM/ [caje]: https://github.com/Tarek701/CajeASM/
A run-down of various syntax elements: A run-down of various syntax elements:
``` ```asm
// this is a comment // this is a comment
/* this is a block comment */ /* this is a block comment */
; this is a more traditional assembly style of comment
; we'll be using this so github's syntax highlighting doesn't blow up
// this is comparible to C's #define my_const 0xDEADBEEF ; this is comparible to C's #define my_const 0xDEADBEEF
[my_const]: 0xDEADBEEF [my_const]: 0xDEADBEEF
// we can then use it in instructions with a @ prefix ; we can then use it in instructions by adding a @ prefix
li a0, @my_const li a0, @my_const
// whitespace is optional ; whitespace is optional
li a0,@myconst li a0,@myconst
// commas can be optional too, ; commas can be optional too,
// but this feature will likely be removed in the future. ; but this feature will likely be removed in the future.
li a0 @myconst li a0 @myconst
// instruction/register names are case-insensitive, as are hex digits ; instruction/register names are case-insensitive, as are hex digits
LI A0, @my_const LI A0, @my_const
LuI a0, 0xDeAd LuI a0, 0xDeAd
// coprocessor 0 registers are case-insensitive as well, ; coprocessor 0 registers are case-insensitive as well,
// though this may change in the future. ; though this may change in the future.
mfc0 a1, CouNT mfc0 a1, CouNT
// labels are defined with a colon and referenced without prefix, as such: ; labels are defined with a colon and referenced without prefix, as such:
my_label: my_label:
b my_label b my_label
nop nop
// directives are prefixed with a dot. ; directives are prefixed with a dot.
// also, labels may be used in .word directives. ; also, labels may be used in .word directives.
.word my_label, 1, 2, 3, 0x4567 .word my_label, 1, 2, 3, 0x4567
// octal numbers are supported ; octal numbers are supported
.short 0177, 0404 .short 0177, 0404
.align // implied argument of 2, for a 2**n=4 byte alignment .align ; implied argument of 2, for a 2**n=4 byte alignment
// loading and storing can be written in several ways (addressing modes) ; loading and storing can be written in several ways (addressing modes)
lw s0, label lw s0, label
lw s1, (s0) lw s1, (s0)
lw s2, 256(s0) lw s2, 256(s0)
lw s3, label(s0) lw s3, label(s0)
// this is currently unsupported however ; this is currently unsupported however
sw s2, label+4 sw s2, label+4
sw s3, label+4(s0) sw s3, label+4(s0)
// relative labels, borrowed from asw (except ours require a suffixing colon) ; relative labels, borrowed from asw (except ours require a suffixing colon)
-: -:
b ++ b ++
nop nop
@ -106,7 +108,7 @@ my_label:
b - b -
nop nop
// TODO: more examples! ; TODO: more examples!
``` ```
## Instructions ## Instructions

103
example.asm
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@ -1,98 +1,97 @@
/* lips example code: fibonacci numbers ; lips example code: fibonacci numbers
* this isn't a particularily useful or realistic example, ; this isn't a particularily useful or realistic example,
* but it demonstrates syntax and various features in lips. ; but it demonstrates syntax and various features in lips.
*/
[max_n]: 47 [max_n]: 47
fib: fib:
// calculate the nth fibonacci number, caching results 1 to 47 to a table ; calculate the nth fibonacci number, caching results 1 to 47 to a table
// only valid for values of n between 0 and 47 inclusive. ; only valid for values of n between 0 and 47 inclusive.
// a0: n ; a0: n
// v0: Fn ; v0: Fn
// branch to return 0 if a0 <= 0. ; branch to return 0 if a0 <= 0.
// the + refers to the next + label, relative to here. ; the + refers to the next + label, relative to here.
// ++ would refer to the + label after that, and so on. ; ++ would refer to the + label after that, and so on.
blez a0, + blez a0, +
// note that this executes even if the branch is taken, ; note that this executes even if the branch is taken,
// due to the single delay slot of this MIPS CPU. ; due to the single delay slot of this MIPS CPU.
// pseudo-instruction clears (sets to 0) the 32-bit value of a register: ; pseudo-instruction clears (sets to 0) the 32-bit value of a register:
cl v0 cl v0
// check if the input is within the bounds specified earlier. ; check if the input is within the bounds specified earlier.
// pseudo-instruction to branch if register > immediate: ; pseudo-instruction to branch if register > immediate:
bgti a0, @max_n, + bgti a0, @max_n, +
// offset the input for use with the look-up table. ; offset the input for use with the look-up table.
// note that this executes even if the branch is taken, ; note that this executes even if the branch is taken,
// but won't break the functionality of the routine either way. ; but won't break the functionality of the routine either way.
// pseudo-instruction translates into an addiu with a negated immediate: ; pseudo-instruction translates into an addiu with a negated immediate:
subiu t0, a0, 1 subiu t0, a0, 1
// multiply by sizeof(word) which is 4, or 1 << 2. ; multiply by sizeof(word) which is 4, or 1 << 2.
sll t0, t0, 2 sll t0, t0, 2
// load the value from the look-up table. ; load the value from the look-up table.
// pseudo-instruction utilizing addressing modes: ; pseudo-instruction utilizing addressing modes:
lw t9, fib_cache(t0) lw t9, fib_cache(t0)
// branch to return the look-up value if it's non-zero, meaning it has been cached. ; branch to return the look-up value if it's non-zero, meaning it has been cached.
bnez t9, + bnez t9, +
// once again, note that this is the delay slot of the branch instruction. ; once again, note that this is the delay slot of the branch instruction.
// pseudo-instruction to copy the 32-bit value of one register to another: ; pseudo-instruction to copy the 32-bit value of one register to another:
mov v0, t9 mov v0, t9
// set up the following loop to calculate the fibonacci number. ; set up the following loop to calculate the fibonacci number.
// pseudo-instruction to load a 32-bit value into a register: ; pseudo-instruction to load a 32-bit value into a register:
li t1, 0 // F(0) li t1, 0 ; F(0)
li t2, 1 // F(1) li t2, 1 ; F(1)
-: // here's a - label referred to later. -: ; here's a - label referred to later.
// - labels are like + labels, except ; - labels are like + labels, except
// they look upwards in the file instead of downwards. ; they look upwards in the file instead of downwards.
// calculate the next fibonacci number. ; calculate the next fibonacci number.
addu t3, t1, t2 addu t3, t1, t2
// push the previous values back, part 1. ; push the previous values back, part 1.
mov t1, t2 mov t1, t2
// iterate to the next number. ; iterate to the next number.
subiu a0, a0, 1 subiu a0, a0, 1
// loop if it hasn't yet reached the nth fibonacci number. ; loop if it hasn't yet reached the nth fibonacci number.
bnez a0, - bnez a0, -
// push the previous values back, part 2. ; push the previous values back, part 2.
// this is put in the branch delay as a simple optimization. ; this is put in the branch delay as a simple optimization.
mov t2, t3 mov t2, t3
// loop finished, copy the result to return. ; loop finished, copy the result to return.
mov v0, t1 mov v0, t1
// cache the result for next time. ; cache the result for next time.
// pseudo-instruction not unlike the previous lw: ; pseudo-instruction not unlike the previous lw:
sw v0, fib_cache(t0) sw v0, fib_cache(t0)
// here's the + label used at the start of the routine. ; here's the + label used at the start of the routine.
+: +:
// return to the function that called this routine. ; return to the function that called this routine.
// when jr is given without any arguments, `jr ra` is implied. ; when jr is given without any arguments, `jr ra` is implied.
jr jr
// there's nothing to do in the delay slot, so don't do anything. ; there's nothing to do in the delay slot, so don't do anything.
// this is necessary, otherwise the next instruction or data ; this is necessary, otherwise the next instruction or data
// following the routine would be executed. ; following the routine would be executed.
// pseudo-instruction to do nothing: ; pseudo-instruction to do nothing:
nop nop
// set up initial values in the look-up table. ; set up initial values in the look-up table.
fib_cache: fib_cache:
// lips doesn't yet have a way to specify "x, n times", ; lips doesn't yet have a way to specify "x, n times",
// so this will do for now. ; so this will do for now.
.word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 .word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
.word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 .word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
.word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 .word 0, 0, 0, 0, 0, 0, 0, 0, 0, 0