Remove the need to provide the maximum number of digits to impl_Display macro

Author: GuillaumeGomez

library/core/src/fmt/num.rs

@@ -208,7 +208,7 @@ static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
  8081828384858687888990919293949596979899";
 
 macro_rules! impl_Display {
-($($t:ident => $size:literal $(as $positive:ident)? named $name:ident,)*;as $u:ident via $conv_fn:ident named $gen_name:ident) => {
+($($t:ident $(as $positive:ident)? named $name:ident,)*;as $u:ident via $conv_fn:ident named $gen_name:ident) => {
 
  $(
  #[stable(feature = "rust1", since = "1.0.0")]
@@ -248,8 +248,9 @@ macro_rules! impl_Display {
  #[cfg(not(feature = "optimize_for_size"))]
 impl $t {
 fn _fmt(mutself: $t, is_nonnegative:bool, f:&mut fmt::Formatter<'_>) -> fmt::Result{
-letmut buf = [MaybeUninit::<u8>::uninit(); $size];
-letmut curr = $size;
+constSIZE:usize = $t::MAX.ilog(10)asusize + 1;
+letmut buf = [MaybeUninit::<u8>::uninit();SIZE];
+letmut curr = SIZE;
 let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
 let lut_ptr = DEC_DIGITS_LUT.as_ptr();
 
@@ -526,16 +527,16 @@ macro_rules! impl_Exp {
 mod imp {
 usesuper::*;
 impl_Display!(
-i8=> 3asu8 named fmt_i8,
-u8=> 3named fmt_u8,
-i16=> 5asu16 named fmt_i16,
-u16=> 5named fmt_u16,
-i32=> 10asu32 named fmt_i32,
-u32=> 10named fmt_u32,
-i64=> 19asu64 named fmt_i64,
-u64=> 20named fmt_u64,
-isize=> 19asusize named fmt_isize,
-usize=> 20named fmt_usize,
+i8asu8 named fmt_i8,
+u8 named fmt_u8,
+i16asu16 named fmt_i16,
+u16 named fmt_u16,
+i32asu32 named fmt_i32,
+u32 named fmt_u32,
+i64asu64 named fmt_i64,
+u64 named fmt_u64,
+isizeasusize named fmt_isize,
+usize named fmt_usize,
 ;asu64 via to_u64 named fmt_u64
 );
 impl_Exp!(
@@ -548,18 +549,18 @@ mod imp {
 mod imp {
 usesuper::*;
 impl_Display!(
-i8=> 3asu8 named fmt_i8,
-u8=> 3named fmt_u8,
-i16=> 5asu16 named fmt_i16,
-u16=> 5named fmt_u16,
-i32=> 10asu32 named fmt_i32,
-u32=> 10named fmt_u32,
-isize=> 19asusize named fmt_isize,
-usize=> 20named fmt_usize,
+i8asu8 named fmt_i8,
+u8 named fmt_u8,
+i16asu16 named fmt_i16,
+u16 named fmt_u16,
+i32asu32 named fmt_i32,
+u32 named fmt_u32,
+isizeasusize named fmt_isize,
+usize named fmt_usize,
 ;asu32 via to_u32 named fmt_u32);
 impl_Display!(
-i64=> 19asu64 named fmt_i64,
-u64=> 20named fmt_u64,
+i64asu64 named fmt_i64,
+u64 named fmt_u64,
 ;asu64 via to_u64 named fmt_u64);
 
 impl_Exp!(i8,u8,i16,u16,i32,u32,isize,usizeasu32 via to_u32 named exp_u32);