@@ -297,11 +297,16 @@ pub fn from_u32(n: u32, buffer: &mut [u8]) -> usize {
297297/// Optimized jeaiii algorithm for u64.
298298#[ inline( always) ]
299299#[ allow( clippy:: collapsible_else_if) ] // reason = "branching is fine-tuned for performance"
300- pub fn from_u64 ( n : u64 , buffer : & mut [ u8 ] ) -> usize {
300+ fn from_u64_impl ( n : u64 , buffer : & mut [ u8 ] , is_signed : bool ) -> usize {
301301 // NOTE: Like before, this optimizes better for large and small
302302 // values if there's a flat comparison with larger values first.
303303 const FACTOR : u64 = 100_0000_0000 ;
304- let buffer = & mut buffer[ ..20 ] ;
304+ // NOTE `i64` takes a max of 19 digits, while `u64` takes a max of 20.
305+ let buffer = if is_signed {
306+ & mut buffer[ ..19 ]
307+ } else {
308+ & mut buffer[ ..20 ]
309+ } ;
305310 if n < 1_0000 {
306311 // 1 to 4 digits
307312 if n >= 100 {
@@ -326,7 +331,7 @@ pub fn from_u64(n: u64, buffer: &mut [u8]) -> usize {
326331 write_digits ! ( @5 -6 buffer, n)
327332 }
328333 } else {
329- // 11-20 digits, can do in 2 steps
334+ // 11-20 digits, can do in 2 steps (11-19 if is signed).
330335 // NOTE: `hi` has to be in `[0, 2^31)`, while `lo` is in `[0, 10^11)`
331336 // So, we can use our `from_u64_small` for hi. For our `lo`, we always
332337 // need to write 10 digits. However, the `jeaiii` algorithm is too
@@ -340,6 +345,23 @@ pub fn from_u64(n: u64, buffer: &mut [u8]) -> usize {
340345 }
341346}
342347
348+ /// Optimized jeaiii algorithm for u64.
349+ #[ inline( always) ]
350+ pub fn from_u64 ( n : u64 , buffer : & mut [ u8 ] ) -> usize {
351+ from_u64_impl ( n, buffer, false )
352+ }
353+
354+ /// Optimized jeaiii algorithm for i64, which must be positive.
355+ ///
356+ /// This value **MUST** have originally been from an `i64`, since it
357+ /// uses `19` for the bounds checked, so this will panic if `>= 10^19`
358+ /// is passed to the function.
359+ #[ inline( always) ]
360+ pub fn from_i64 ( n : u64 , buffer : & mut [ u8 ] ) -> usize {
361+ debug_assert ! ( n <= 1000_0000_0000_0000_0000u64 ) ;
362+ from_u64_impl ( n, buffer, true )
363+ }
364+
343365/// Optimized jeaiii algorithm for u128.
344366#[ inline( always) ]
345367#[ allow( clippy:: collapsible_else_if) ] // reason = "branching is fine-tuned for performance"
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