140 lines
5.5 KiB
Rust
140 lines
5.5 KiB
Rust
use prolog::and_stack::*;
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use prolog::instructions::*;
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use std::ops::IndexMut;
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type Trail = Vec<(Ref, HeapCellValue)>;
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pub(crate) struct RedirectInfo {
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trail: Trail
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}
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pub(crate) trait CopierTarget
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{
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fn source(&self) -> usize;
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fn threshold(&self) -> usize;
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fn push(&mut self, HeapCellValue);
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fn store(&self, Addr) -> Addr;
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fn deref(&self, Addr) -> Addr;
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fn stack(&mut self) -> &mut AndStack;
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fn unwind_trail(&mut self, redirect: RedirectInfo)
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where Self: IndexMut<usize, Output=HeapCellValue>
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{
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for (r, hcv) in redirect.trail {
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match r {
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Ref::HeapCell(hc) => self[hc] = hcv.clone(),
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Ref::StackCell(fr, sc) => self.stack()[fr][sc] = hcv.as_addr(0)
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}
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}
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}
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// duplicate_term_impl(L1, L2) uses Cheney's algorithm to copy the term
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// at L1 to L2. trail is kept to restore the innards of L1 after
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// it's been copied to L2.
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fn duplicate_term_impl(&mut self, addr: Addr) -> RedirectInfo
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where Self: IndexMut<usize, Output=HeapCellValue>
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{
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let mut trail = Trail::new();
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let mut scan = self.source();
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let old_h = self.threshold();
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self.push(HeapCellValue::Addr(addr));
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while scan < self.threshold() {
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match self[scan].clone() {
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HeapCellValue::NamedStr(..) =>
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scan += 1,
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HeapCellValue::Addr(a) =>
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match a.clone() {
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Addr::Lis(a) => {
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if let HeapCellValue::Addr(Addr::Lis(b)) = self[a].clone() {
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if b >= old_h {
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self[scan] = HeapCellValue::Addr(Addr::Lis(b));
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scan += 1;
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continue;
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}
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}
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let threshold = self.threshold();
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self[scan] = HeapCellValue::Addr(Addr::Lis(threshold));
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let hcv = self[a].clone();
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self.push(hcv);
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let hcv = self[a+1].clone();
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self.push(hcv);
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trail.push((Ref::HeapCell(a), self[a].clone()));
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self[a] = HeapCellValue::Addr(Addr::Lis(threshold));
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scan += 1;
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},
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Addr::HeapCell(_) | Addr::StackCell(_, _) => {
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let ra = a;
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let rd = self.store(self.deref(ra.clone()));
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match rd.clone() {
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Addr::HeapCell(hc) if hc >= old_h => {
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self[scan] = HeapCellValue::Addr(rd);
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scan += 1;
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},
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_ if ra == rd => {
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self[scan] = HeapCellValue::Addr(Addr::HeapCell(scan));
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if let Addr::HeapCell(hc) = ra.clone() {
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self[hc] = HeapCellValue::Addr(Addr::HeapCell(scan));
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trail.push((Ref::HeapCell(hc),
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HeapCellValue::Addr(Addr::HeapCell(hc))));
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} else if let Addr::StackCell(fr, sc) = ra {
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self.stack()[fr][sc] = Addr::HeapCell(scan);
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trail.push((Ref::StackCell(fr, sc),
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HeapCellValue::Addr(Addr::StackCell(fr, sc))));
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}
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scan += 1;
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},
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_ => self[scan] = HeapCellValue::Addr(rd)
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};
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},
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Addr::Str(s) => {
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match self[s].clone() {
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HeapCellValue::NamedStr(arity, name, fixity) => {
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let threshold = self.threshold();
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self[scan] = HeapCellValue::Addr(Addr::Str(threshold));
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self[s] = HeapCellValue::Addr(Addr::Str(threshold));
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trail.push((Ref::HeapCell(s),
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HeapCellValue::NamedStr(arity, name.clone(), fixity)));
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self.push(HeapCellValue::NamedStr(arity, name, fixity));
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for i in 0 .. arity {
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let hcv = self[s + 1 + i].clone();
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self.push(hcv);
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}
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},
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HeapCellValue::Addr(Addr::Str(o)) =>
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self[scan] = HeapCellValue::Addr(Addr::Str(o)),
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_ => {}
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};
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scan += 1;
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},
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Addr::Con(_) => scan += 1
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}
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}
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}
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RedirectInfo { trail }
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}
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fn duplicate_term(&mut self, addr: Addr)
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where Self: IndexMut<usize, Output=HeapCellValue>
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{
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let redirect = self.duplicate_term_impl(addr);
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self.unwind_trail(redirect);
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}
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}
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