Rollup merge of #125606 - diondokter:opt-size-int-fmt, r=cuviper · model-checking/verify-rust-std@3b60335 (original) (raw)
`@@ -212,6 +212,7 @@ static DEC_DIGITS_LUT: &[u8; 200] = b"0001020304050607080910111213141516171819\
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`macro_rules! impl_Display {
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`($($t:ident),* as u:identviau:ident via u:identviaconv_fn:ident named $name:ident) => {
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#[cfg(not(feature = "optimize_for_size"))]
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`fn name(mutn:name(mut n: name(mutn:u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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`// 2^128 is about 3*10^38, so 39 gives an extra byte of space
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`let mut buf = [MaybeUninit::::uninit(); 39];
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`@@ -277,6 +278,38 @@ macro_rules! impl_Display {
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` f.pad_integral(is_nonnegative, "", buf_slice)
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`}
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#[cfg(feature = "optimize_for_size")]
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fn name(mutn:name(mut n: name(mutn:u, is_nonnegative: bool, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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// 2^128 is about 3*10^38, so 39 gives an extra byte of space
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let mut buf = [MaybeUninit::::uninit(); 39];
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let mut curr = buf.len();
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let buf_ptr = MaybeUninit::slice_as_mut_ptr(&mut buf);
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// SAFETY: To show that it's OK to copy into buf_ptr, notice that at the beginning
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// curr == buf.len() == 39 > log(n) since n < 2^128 < 10^39, and at
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// each step this is kept the same as n is divided. Since n is always
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// non-negative, this means that curr > 0 so buf_ptr[curr..curr + 1]
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// is safe to access.
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unsafe {
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loop {
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curr -= 1;
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buf_ptr.add(curr).write((n % 10) as u8 + b'0');
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n /= 10;
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if n == 0 {
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break;
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}
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}
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}
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// SAFETY: curr > 0 (since we made buf large enough), and all the chars are valid UTF-8
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let buf_slice = unsafe {
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str::from_utf8_unchecked(
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slice::from_raw_parts(buf_ptr.add(curr), buf.len() - curr))
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};
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f.pad_integral(is_nonnegative, "", buf_slice)
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}
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` $(#[stable(feature = "rust1", since = "1.0.0")]
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`impl fmt::Display for $t {
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` #[allow(unused_comparisons)]
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