Sync to vitaut/zmij@408ebfb

Author: dtolnay

README.md

@@ -11,7 +11,7 @@ numbers to decimal strings.
 This Rust implementation is a line-by-line port of Victor Zverovich's
 implementation in C++, [https://github.com/vitaut/zmij][upstream].
 
-[upstream]: https://github.com/vitaut/zmij/tree/98d01d3bc6aceb80b8420ea13874e0ae9af0c9e8
+[upstream]: https://github.com/vitaut/zmij/tree/408ebfb0c70579895e12864aeb00561ef15729e3
 
 ## Example
 

src/lib.rs

@@ -636,7 +636,7 @@ unsafe fn write_significand17(
         // zero. buffer points to the second place in the output buffer to allow
         // for the insertion of the decimal point, so we can use the first place
         // as scratch.
-        buffer = unsafe { buffer.add(usize::from(has17digits)) };
+        buffer = unsafe { buffer.offset(isize::from(has17digits) - 1) };
         unsafe {
             *buffer.add(16) = last_digit as u8 + b'0';
         }