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correct and simplify compute_pstr_size

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This commit is contained in:
Mark Thom
2025-04-12 00:22:29 -07:00
committed by Mark Thom
parent e20363b462
commit 16b3bea48e
1 changed files with 17 additions and 32 deletions
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51
src/machine/heap.rs
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@@ -92,7 +92,10 @@ pub struct HeapStringScan<'a> {
// return the string at ptr and the tail location relative to ptr. // return the string at ptr and the tail location relative to ptr.
unsafe fn scan_slice_to_str(heap_slice: &[u8]) -> HeapStringScan { unsafe fn scan_slice_to_str(heap_slice: &[u8]) -> HeapStringScan {
let string_len = heap_slice.iter().position(|b| *b == 0u8).unwrap(); let string_len = heap_slice
.iter()
.position(|b| *b == 0u8)
.unwrap_or(heap_slice.len());
let zero_byte_addr = heap_slice.as_ptr().add(string_len); let zero_byte_addr = heap_slice.as_ptr().add(string_len);
let sentinel_len = pstr_sentinel_length(zero_byte_addr as usize); let sentinel_len = pstr_sentinel_length(zero_byte_addr as usize);
@@ -889,44 +892,26 @@ impl Heap {
/// Returns the number of bytes needed to store `src` as a `PStr`. /// Returns the number of bytes needed to store `src` as a `PStr`.
/// Assumes the string will be allocated on a ALIGN-byte boundary. /// Assumes the string will be allocated on a ALIGN-byte boundary.
pub(crate) fn compute_pstr_size(src: &str) -> usize { pub(crate) fn compute_pstr_size(src: &str) -> usize {
if src.is_empty() {
return 0;
}
let mut byte_size = 0; let mut byte_size = 0;
let mut null_idx = 0; let mut src_bytes = src.as_bytes();
loop { while !src_bytes.is_empty() {
let src_bytes = src.as_bytes(); if src_bytes[0] == 0 {
// push a list_loc_as_cell! and null char atom to the heap and continue.
while null_idx < src_bytes.len() { byte_size += heap_index!(2);
if src_bytes[null_idx] == 0u8 { src_bytes = &src_bytes[1..];
break; continue;
} }
null_idx += 1; let HeapStringScan { string, tail_idx } = unsafe { scan_slice_to_str(src_bytes) };
src_bytes = &src_bytes[string.len()..];
byte_size += heap_index!(tail_idx);
} }
byte_size += null_idx + pstr_sentinel_length(null_idx); // add 1 cell to make up for the final tail cell. if src == "" it's written to the heap as
// empty_list_as_cell!() and the pstr_size is 0 + heap_index!(1).
// each partial string must be buffered from its tail cell byte_size + heap_index!(1)
// by at least two null bytes so one of them may be used
// to mark partial strings e.g. during iteration
if (null_idx + 1).next_multiple_of(ALIGN) == null_idx + 1 {
byte_size += 2 * size_of::<HeapCellValue>();
} else {
byte_size += size_of::<HeapCellValue>();
}
if null_idx + 1 >= src.len() {
break;
} else {
null_idx += 1;
}
}
byte_size
} }
pub(crate) const fn compute_functor_byte_size(functor: &[FunctorElement]) -> usize { pub(crate) const fn compute_functor_byte_size(functor: &[FunctorElement]) -> usize {