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[skrifa] tthint: adjust DELTAP/DELTAC limits #1353

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Feb 11, 2025
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[skrifa] tthint: adjust DELTAP/DELTAC limits #1353

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14 changes: 8 additions & 6 deletions skrifa/src/outline/glyf/hint/engine/delta.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,9 +32,10 @@ impl Engine<'_> {
let ppem = gs.ppem as u32;
let point_count = gs.zp0().points.len();
let n = self.value_stack.pop_count_checked()?;
// Additionally limit n to the number of points in zp0 since
// we don't expect to modify a point more than once
let n = n.min(point_count);
// Each exception requires two values on the stack so limit our
// count to prevent looping in non-pedantic mode (where the stack ops
// will produce 0 instead of an underflow error)
let n = n.min(self.value_stack.len() / 2);
let bias = match opcode {
Opcode::DELTAP2 => 16,
Opcode::DELTAP3 => 32,
Expand Down Expand Up @@ -98,9 +99,10 @@ impl Engine<'_> {
let gs = &mut self.graphics;
let ppem = gs.ppem as u32;
let n = self.value_stack.pop_count_checked()?;
// Additionally limit n to the number of CVT entries since we
// don't expect to modify an entry more than once
let n = n.min(self.cvt.len());
// Each exception requires two values on the stack so limit our
// count to prevent looping in non-pedantic mode (where the stack ops
// will produce 0 instead of an underflow error)
let n = n.min(self.value_stack.len() / 2);
let bias = match opcode {
Opcode::DELTAC2 => 16,
Opcode::DELTAC3 => 32,
Expand Down