compiler help in fmt::Display of integers

Author: pascaldekloe

library/core/src/fmt/num.rs

@@ -255,12 +255,12 @@ macro_rules! impl_Display {
 
                     let quad = remain % 100_00;
                     remain /= 100_00;
-                    let p1 = (quad / 100) as usize * 2;
-                    let p2 = (quad % 100) as usize * 2;
-                    buf[offset + 0].write(DEC_DIGITS_LUT[p1 + 0]);
-                    buf[offset + 1].write(DEC_DIGITS_LUT[p1 + 1]);
-                    buf[offset + 2].write(DEC_DIGITS_LUT[p2 + 0]);
-                    buf[offset + 3].write(DEC_DIGITS_LUT[p2 + 1]);
+                    let i1 = (quad / 100) as usize;
+                    let i2 = (quad % 100) as usize;
+                    buf[offset + 0].write(DEC_DIGITS_LUT[i1 * 2 + 0]);
+                    buf[offset + 1].write(DEC_DIGITS_LUT[i1 * 2 + 1]);
+                    buf[offset + 2].write(DEC_DIGITS_LUT[i2 * 2 + 0]);
+                    buf[offset + 3].write(DEC_DIGITS_LUT[i2 * 2 + 1]);
                 }
 
                 // Format per two digits from the lookup table.
@@ -270,24 +270,24 @@ macro_rules! impl_Display {
                     unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
                     offset -= 2;
 
-                    let p = (remain % 100) as usize * 2;
+                    let i = (remain % 100) as usize;
                     remain /= 100;
-                    buf[offset + 0].write(DEC_DIGITS_LUT[p + 0]);
-                    buf[offset + 1].write(DEC_DIGITS_LUT[p + 1]);
+                    buf[offset + 0].write(DEC_DIGITS_LUT[i * 2 + 0]);
+                    buf[offset + 1].write(DEC_DIGITS_LUT[i * 2 + 1]);
                 }
 
                 // Format the last remaining digit, if any.
-                if offset != 0 && remain != 0 || offset == MAX_DEC_N {
+                if offset != 0 && remain != 0 || self == 0 {
                     // SAFETY: Offset from the initial buf.len() gets deducted
                     // with underflow checks exclusively.
                     unsafe { core::hint::assert_unchecked(offset <= buf.len()) }
                     offset -= 1;
 
                     // Either the compiler sees that remain < 10, or it prevents
                     // a boundary check up next.
-                    let p = (remain % 10) as usize * 2;
+                    let i = (remain & 15) as usize;
                     // not used: remain = 0;
-                    buf[offset].write(DEC_DIGITS_LUT[p + 1]);
+                    buf[offset].write(DEC_DIGITS_LUT[i * 2 + 1]);
                 }
 
                 // SAFETY: All buf content since offset is set with bytes form