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-rw-r--r--third_party/rust/syn/src/bigint.rs66
1 files changed, 66 insertions, 0 deletions
diff --git a/third_party/rust/syn/src/bigint.rs b/third_party/rust/syn/src/bigint.rs
new file mode 100644
index 0000000000..5397d6beee
--- /dev/null
+++ b/third_party/rust/syn/src/bigint.rs
@@ -0,0 +1,66 @@
+use std::ops::{AddAssign, MulAssign};
+
+// For implementing base10_digits() accessor on LitInt.
+pub struct BigInt {
+ digits: Vec<u8>,
+}
+
+impl BigInt {
+ pub fn new() -> Self {
+ BigInt { digits: Vec::new() }
+ }
+
+ pub fn to_string(&self) -> String {
+ let mut repr = String::with_capacity(self.digits.len());
+
+ let mut has_nonzero = false;
+ for digit in self.digits.iter().rev() {
+ has_nonzero |= *digit != 0;
+ if has_nonzero {
+ repr.push((*digit + b'0') as char);
+ }
+ }
+
+ if repr.is_empty() {
+ repr.push('0');
+ }
+
+ repr
+ }
+
+ fn reserve_two_digits(&mut self) {
+ let len = self.digits.len();
+ let desired =
+ len + !self.digits.ends_with(&[0, 0]) as usize + !self.digits.ends_with(&[0]) as usize;
+ self.digits.resize(desired, 0);
+ }
+}
+
+impl AddAssign<u8> for BigInt {
+ // Assumes increment <16.
+ fn add_assign(&mut self, mut increment: u8) {
+ self.reserve_two_digits();
+
+ let mut i = 0;
+ while increment > 0 {
+ let sum = self.digits[i] + increment;
+ self.digits[i] = sum % 10;
+ increment = sum / 10;
+ i += 1;
+ }
+ }
+}
+
+impl MulAssign<u8> for BigInt {
+ // Assumes base <=16.
+ fn mul_assign(&mut self, base: u8) {
+ self.reserve_two_digits();
+
+ let mut carry = 0;
+ for digit in &mut self.digits {
+ let prod = *digit * base + carry;
+ *digit = prod % 10;
+ carry = prod / 10;
+ }
+ }
+}