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fix potential uint overflow #243

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fix potential uint overflow #243

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12 changes: 8 additions & 4 deletions src/stdlib/native/int/lib.no
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,8 @@ struct Uint8 {
fn Uint8.new(val: Field) -> Uint8 {
let bit_len = 8;

bits::check_field_size(bit_len);
// has to ensure multiply won't overflow prime field
bits::check_field_size(bit_len * 2);
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isn't it off by one?

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Inside check_field_size, it checks the prime field is strictly greater than bit_len * 2:

if to_cmp >= bit_len {
    return Err(Error::new(
        "constraint-generation",
        ErrorKind::AssertionFailed,
        span,
    ));
}

So the prime field bit len is ensured to have at least one more bit than the test value.


// range check
let ignore_ = bits::to_bits(bit_len, val);
Expand All @@ -33,7 +34,8 @@ struct Uint16 {
fn Uint16.new(val: Field) -> Uint16 {
let bit_len = 16;

bits::check_field_size(bit_len);
// has to ensure multiply won't overflow prime field
bits::check_field_size(bit_len * 2);

// range check
let ignore_ = bits::to_bits(bit_len, val);
Expand All @@ -52,7 +54,8 @@ struct Uint32 {
fn Uint32.new(val: Field) -> Uint32 {
let bit_len = 32;

bits::check_field_size(bit_len);
// has to ensure multiply won't overflow prime field
bits::check_field_size(bit_len * 2);

// range check
let ignore_ = bits::to_bits(bit_len, val);
Expand All @@ -71,7 +74,8 @@ struct Uint64 {
fn Uint64.new(val: Field) -> Uint64 {
let bit_len = 64;

bits::check_field_size(bit_len);
// has to ensure multiply won't overflow prime field
bits::check_field_size(bit_len * 2);

// range check
let ignore_ = bits::to_bits(bit_len, val);
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