Introduce the 'true' and 'false' conditions

master
Nat Lasseter 4 years ago
parent 453f421bae
commit 12e37d4335
  1. 3
      README.md
  2. 11
      crsn/src/asm/instr/cond.rs
  3. 2
      crsn/src/runtime/frame/status.rs
  4. 24
      examples/test_cond.csn

@ -98,6 +98,8 @@ These keywords (among others) are used in conditional branches to specify flag t
- `nem`, `nempty` … Not empty
- `eof` … EOF
- `neof` … Not EOF
- `true`, `always`, `else` … Always true
- `false`, `never` … Always false
# Syntax
@ -207,6 +209,7 @@ Conditonal branches are written like this:
then only one branch is taken - there is no fall-through.
- The definition order is preserved, i.e. if the `inval` flag is to be checked, it should be done
before checking e.g. `nz`, which is, incidentally, true by default, because most flags are cleared by instructions that affects flags.
- `else` can be used as a final choice of branch that will always be taken.
## Routines

@ -106,6 +106,10 @@ pub enum Cond {
Eof,
/// Not empty
NotEof,
// Always true, for eg. (else? ...)
True,
/// Always false
False,
}
pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result<Cond, CrsnError> {
@ -134,6 +138,8 @@ pub fn parse_cond(text: &str, pos: &SourcePosition) -> Result<Cond, CrsnError> {
"neof" => Cond::NotEof,
"ov" => Cond::Overflow,
"nov" => Cond::NotOverflow,
"true" | "always" | "else" => Cond::True,
"false" | "never" => Cond::False,
_ => {
return Err(CrsnError::Parse(format!("Unknown cond: {}", text).into(), pos.clone()));
}
@ -174,6 +180,8 @@ impl Display for Cond {
Cond::Valid => "valid",
Cond::Eof => "eof",
Cond::NotEof => "neof",
Cond::True => "true",
Cond::False => "false",
})
}
}
@ -214,6 +222,9 @@ impl Not for Cond {
Cond::NotEof => Cond::Eof,
Cond::Eof => Cond::NotEof,
Cond::True => Cond::False,
Cond::False => Cond::True,
}
}
}

@ -115,6 +115,8 @@ impl StatusFlags {
Cond::NotEmpty => !self.empty,
Cond::Eof => self.eof,
Cond::NotEof => !self.eof,
Cond::True => true,
Cond::False => false,
}
}

@ -0,0 +1,24 @@
(
(ld r8 0)
(ld r0 1
(true? (add r8 1))
)
(sub r0 1
(pos? (fault))
(else? (add r8 1))
)
(nop
(always? (add r8 1))
)
(nop
(never? (fault))
)
(cmp r8 3
(ne? (fault))
)
)
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