vendor/bstr-1.10.0/src/ascii.rs - toolchain/rustc - Git at Google

 // The following ~400 lines of code exists for exactly one purpose, which is
 // to optimize this code:
 //
 //     byte_slice.iter().position(|&b| b > 0x7F).unwrap_or(byte_slice.len())
 //
 // Yes... Overengineered is a word that comes to mind, but this is effectively
 // a very similar problem to memchr, and virtually nobody has been able to
 // resist optimizing the crap out of that (except for perhaps the BSD and MUSL
 // folks). In particular, this routine makes a very common case (ASCII) very
 // fast, which seems worth it. We do stop short of adding AVX variants of the
 // code below in order to retain our sanity and also to avoid needing to deal
 // with runtime target feature detection. RESIST!
 //
 // In order to understand the SIMD version below, it would be good to read this
 // comment describing how my memchr routine works:
 // https://github.com/BurntSushi/rust-memchr/blob/b0a29f267f4a7fad8ffcc8fe8377a06498202883/src/x86/sse2.rs#L19-L106
 //
 // The primary difference with memchr is that for ASCII, we can do a bit less
 // work. In particular, we don't need to detect the presence of a specific
 // byte, but rather, whether any byte has its most significant bit set. That
 // means we can effectively skip the _mm_cmpeq_epi8 step and jump straight to
 // _mm_movemask_epi8.

 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 const USIZE_BYTES: usize = core::mem::size_of::<usize>();
 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 const FALLBACK_LOOP_SIZE: usize = 2 * USIZE_BYTES;

 // This is a mask where the most significant bit of each byte in the usize
 // is set. We test this bit to determine whether a character is ASCII or not.
 // Namely, a single byte is regarded as an ASCII codepoint if and only if it's
 // most significant bit is not set.
 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 const ASCII_MASK_U64: u64 = 0x8080808080808080;
 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 const ASCII_MASK: usize = ASCII_MASK_U64 as usize;

 /// Returns the index of the first non ASCII byte in the given slice.
 ///
 /// If slice only contains ASCII bytes, then the length of the slice is
 /// returned.
 pub fn first_non_ascii_byte(slice: &[u8]) -> usize {
     #[cfg(any(miri, not(target_arch = "x86_64")))]
     {
         first_non_ascii_byte_fallback(slice)
     }

     #[cfg(all(not(miri), target_arch = "x86_64"))]
     {
         first_non_ascii_byte_sse2(slice)
     }
 }

 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 fn first_non_ascii_byte_fallback(slice: &[u8]) -> usize {
     let align = USIZE_BYTES - 1;
     let start_ptr = slice.as_ptr();
     let end_ptr = slice[slice.len()..].as_ptr();
     let mut ptr = start_ptr;

     unsafe {
         if slice.len() < USIZE_BYTES {
             return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
         }

         let chunk = read_unaligned_usize(ptr);
         let mask = chunk & ASCII_MASK;
         if mask != 0 {
             return first_non_ascii_byte_mask(mask);
         }

         ptr = ptr_add(ptr, USIZE_BYTES - (start_ptr as usize & align));
         debug_assert!(ptr > start_ptr);
         debug_assert!(ptr_sub(end_ptr, USIZE_BYTES) >= start_ptr);
         if slice.len() >= FALLBACK_LOOP_SIZE {
             while ptr <= ptr_sub(end_ptr, FALLBACK_LOOP_SIZE) {
                 debug_assert_eq!(0, (ptr as usize) % USIZE_BYTES);

                 let a = *(ptr as *const usize);
                 let b = *(ptr_add(ptr, USIZE_BYTES) as *const usize);
                 if (a | b) & ASCII_MASK != 0 {
                     // What a kludge. We wrap the position finding code into
                     // a non-inlineable function, which makes the codegen in
                     // the tight loop above a bit better by avoiding a
                     // couple extra movs. We pay for it by two additional
                     // stores, but only in the case of finding a non-ASCII
                     // byte.
                     #[inline(never)]
                     unsafe fn findpos(
                         start_ptr: *const u8,
                         ptr: *const u8,
                     ) -> usize {
                         let a = *(ptr as *const usize);
                         let b = *(ptr_add(ptr, USIZE_BYTES) as *const usize);

                         let mut at = sub(ptr, start_ptr);
                         let maska = a & ASCII_MASK;
                         if maska != 0 {
                             return at + first_non_ascii_byte_mask(maska);
                         }

                         at += USIZE_BYTES;
                         let maskb = b & ASCII_MASK;
                         debug_assert!(maskb != 0);
                         return at + first_non_ascii_byte_mask(maskb);
                     }
                     return findpos(start_ptr, ptr);
                 }
                 ptr = ptr_add(ptr, FALLBACK_LOOP_SIZE);
             }
         }
         first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
     }
 }

 #[cfg(all(not(miri), target_arch = "x86_64"))]
 fn first_non_ascii_byte_sse2(slice: &[u8]) -> usize {
     use core::arch::x86_64::*;

     const VECTOR_SIZE: usize = core::mem::size_of::<__m128i>();
     const VECTOR_ALIGN: usize = VECTOR_SIZE - 1;
     const VECTOR_LOOP_SIZE: usize = 4 * VECTOR_SIZE;

     let start_ptr = slice.as_ptr();
     let end_ptr = slice[slice.len()..].as_ptr();
     let mut ptr = start_ptr;

     unsafe {
         if slice.len() < VECTOR_SIZE {
             return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
         }

         let chunk = _mm_loadu_si128(ptr as *const __m128i);
         let mask = _mm_movemask_epi8(chunk);
         if mask != 0 {
             return mask.trailing_zeros() as usize;
         }

         ptr = ptr.add(VECTOR_SIZE - (start_ptr as usize & VECTOR_ALIGN));
         debug_assert!(ptr > start_ptr);
         debug_assert!(end_ptr.sub(VECTOR_SIZE) >= start_ptr);
         if slice.len() >= VECTOR_LOOP_SIZE {
             while ptr <= ptr_sub(end_ptr, VECTOR_LOOP_SIZE) {
                 debug_assert_eq!(0, (ptr as usize) % VECTOR_SIZE);

                 let a = _mm_load_si128(ptr as *const __m128i);
                 let b = _mm_load_si128(ptr.add(VECTOR_SIZE) as *const __m128i);
                 let c =
                     _mm_load_si128(ptr.add(2 * VECTOR_SIZE) as *const __m128i);
                 let d =
                     _mm_load_si128(ptr.add(3 * VECTOR_SIZE) as *const __m128i);

                 let or1 = _mm_or_si128(a, b);
                 let or2 = _mm_or_si128(c, d);
                 let or3 = _mm_or_si128(or1, or2);
                 if _mm_movemask_epi8(or3) != 0 {
                     let mut at = sub(ptr, start_ptr);
                     let mask = _mm_movemask_epi8(a);
                     if mask != 0 {
                         return at + mask.trailing_zeros() as usize;
                     }

                     at += VECTOR_SIZE;
                     let mask = _mm_movemask_epi8(b);
                     if mask != 0 {
                         return at + mask.trailing_zeros() as usize;
                     }

                     at += VECTOR_SIZE;
                     let mask = _mm_movemask_epi8(c);
                     if mask != 0 {
                         return at + mask.trailing_zeros() as usize;
                     }

                     at += VECTOR_SIZE;
                     let mask = _mm_movemask_epi8(d);
                     debug_assert!(mask != 0);
                     return at + mask.trailing_zeros() as usize;
                 }
                 ptr = ptr_add(ptr, VECTOR_LOOP_SIZE);
             }
         }
         while ptr <= end_ptr.sub(VECTOR_SIZE) {
             debug_assert!(sub(end_ptr, ptr) >= VECTOR_SIZE);

             let chunk = _mm_loadu_si128(ptr as *const __m128i);
             let mask = _mm_movemask_epi8(chunk);
             if mask != 0 {
                 return sub(ptr, start_ptr) + mask.trailing_zeros() as usize;
             }
             ptr = ptr.add(VECTOR_SIZE);
         }
         first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
     }
 }

 #[inline(always)]
 unsafe fn first_non_ascii_byte_slow(
     start_ptr: *const u8,
     end_ptr: *const u8,
     mut ptr: *const u8,
 ) -> usize {
     debug_assert!(start_ptr <= ptr);
     debug_assert!(ptr <= end_ptr);

     while ptr < end_ptr {
         if *ptr > 0x7F {
             return sub(ptr, start_ptr);
         }
         ptr = ptr.offset(1);
     }
     sub(end_ptr, start_ptr)
 }

 /// Compute the position of the first ASCII byte in the given mask.
 ///
 /// The mask should be computed by `chunk & ASCII_MASK`, where `chunk` is
 /// 8 contiguous bytes of the slice being checked where *at least* one of those
 /// bytes is not an ASCII byte.
 ///
 /// The position returned is always in the inclusive range [0, 7].
 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 fn first_non_ascii_byte_mask(mask: usize) -> usize {
     #[cfg(target_endian = "little")]
     {
         mask.trailing_zeros() as usize / 8
     }
     #[cfg(target_endian = "big")]
     {
         mask.leading_zeros() as usize / 8
     }
 }

 /// Increment the given pointer by the given amount.
 unsafe fn ptr_add(ptr: *const u8, amt: usize) -> *const u8 {
     debug_assert!(amt < ::core::isize::MAX as usize);
     ptr.offset(amt as isize)
 }

 /// Decrement the given pointer by the given amount.
 unsafe fn ptr_sub(ptr: *const u8, amt: usize) -> *const u8 {
     debug_assert!(amt < ::core::isize::MAX as usize);
     ptr.offset((amt as isize).wrapping_neg())
 }

 #[cfg(any(test, miri, not(target_arch = "x86_64")))]
 unsafe fn read_unaligned_usize(ptr: *const u8) -> usize {
     use core::ptr;

     let mut n: usize = 0;
     ptr::copy_nonoverlapping(ptr, &mut n as *mut _ as *mut u8, USIZE_BYTES);
     n
 }

 /// Subtract `b` from `a` and return the difference. `a` should be greater than
 /// or equal to `b`.
 fn sub(a: *const u8, b: *const u8) -> usize {
     debug_assert!(a >= b);
     (a as usize) - (b as usize)
 }

 #[cfg(test)]
 mod tests {
     use super::*;

     // Our testing approach here is to try and exhaustively test every case.
     // This includes the position at which a non-ASCII byte occurs in addition
     // to the alignment of the slice that we're searching.

     #[test]
     fn positive_fallback_forward() {
         for i in 0..517 {
             let s = "a".repeat(i);
             assert_eq!(
                 i,
                 first_non_ascii_byte_fallback(s.as_bytes()),
                 "i: {:?}, len: {:?}, s: {:?}",
                 i,
                 s.len(),
                 s
             );
         }
     }

     #[test]
     #[cfg(target_arch = "x86_64")]
     #[cfg(not(miri))]
     fn positive_sse2_forward() {
         for i in 0..517 {
             let b = "a".repeat(i).into_bytes();
             assert_eq!(b.len(), first_non_ascii_byte_sse2(&b));
         }
     }

     #[test]
     #[cfg(not(miri))]
     fn negative_fallback_forward() {
         for i in 0..517 {
             for align in 0..65 {
                 let mut s = "a".repeat(i);
                 s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
                 let s = s.get(align..).unwrap_or("");
                 assert_eq!(
                     i.saturating_sub(align),
                     first_non_ascii_byte_fallback(s.as_bytes()),
                     "i: {:?}, align: {:?}, len: {:?}, s: {:?}",
                     i,
                     align,
                     s.len(),
                     s
                 );
             }
         }
     }

     #[test]
     #[cfg(target_arch = "x86_64")]
     #[cfg(not(miri))]
     fn negative_sse2_forward() {
         for i in 0..517 {
             for align in 0..65 {
                 let mut s = "a".repeat(i);
                 s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
                 let s = s.get(align..).unwrap_or("");
                 assert_eq!(
                     i.saturating_sub(align),
                     first_non_ascii_byte_sse2(s.as_bytes()),
                     "i: {:?}, align: {:?}, len: {:?}, s: {:?}",
                     i,
                     align,
                     s.len(),
                     s
                 );
             }
         }
     }
 }
	// The following ~400 lines of code exists for exactly one purpose, which is
	// to optimize this code:
	//
	// byte_slice.iter().position(\|&b\| b > 0x7F).unwrap_or(byte_slice.len())
	//
	// Yes... Overengineered is a word that comes to mind, but this is effectively
	// a very similar problem to memchr, and virtually nobody has been able to
	// resist optimizing the crap out of that (except for perhaps the BSD and MUSL
	// folks). In particular, this routine makes a very common case (ASCII) very
	// fast, which seems worth it. We do stop short of adding AVX variants of the
	// code below in order to retain our sanity and also to avoid needing to deal
	// with runtime target feature detection. RESIST!
	//
	// In order to understand the SIMD version below, it would be good to read this
	// comment describing how my memchr routine works:
	// https://github.com/BurntSushi/rust-memchr/blob/b0a29f267f4a7fad8ffcc8fe8377a06498202883/src/x86/sse2.rs#L19-L106
	//
	// The primary difference with memchr is that for ASCII, we can do a bit less
	// work. In particular, we don't need to detect the presence of a specific
	// byte, but rather, whether any byte has its most significant bit set. That
	// means we can effectively skip the _mm_cmpeq_epi8 step and jump straight to
	// _mm_movemask_epi8.

	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	const USIZE_BYTES: usize = core::mem::size_of::<usize>();
	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	const FALLBACK_LOOP_SIZE: usize = 2 * USIZE_BYTES;

	// This is a mask where the most significant bit of each byte in the usize
	// is set. We test this bit to determine whether a character is ASCII or not.
	// Namely, a single byte is regarded as an ASCII codepoint if and only if it's
	// most significant bit is not set.
	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	const ASCII_MASK_U64: u64 = 0x8080808080808080;
	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	const ASCII_MASK: usize = ASCII_MASK_U64 as usize;

	/// Returns the index of the first non ASCII byte in the given slice.
	///
	/// If slice only contains ASCII bytes, then the length of the slice is
	/// returned.
	pub fn first_non_ascii_byte(slice: &[u8]) -> usize {
	#[cfg(any(miri, not(target_arch = "x86_64")))]
	{
	first_non_ascii_byte_fallback(slice)
	}

	#[cfg(all(not(miri), target_arch = "x86_64"))]
	{
	first_non_ascii_byte_sse2(slice)
	}
	}

	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	fn first_non_ascii_byte_fallback(slice: &[u8]) -> usize {
	let align = USIZE_BYTES - 1;
	let start_ptr = slice.as_ptr();
	let end_ptr = slice[slice.len()..].as_ptr();
	let mut ptr = start_ptr;

	unsafe {
	if slice.len() < USIZE_BYTES {
	return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
	}

	let chunk = read_unaligned_usize(ptr);
	let mask = chunk & ASCII_MASK;
	if mask != 0 {
	return first_non_ascii_byte_mask(mask);
	}

	ptr = ptr_add(ptr, USIZE_BYTES - (start_ptr as usize & align));
	debug_assert!(ptr > start_ptr);
	debug_assert!(ptr_sub(end_ptr, USIZE_BYTES) >= start_ptr);
	if slice.len() >= FALLBACK_LOOP_SIZE {
	while ptr <= ptr_sub(end_ptr, FALLBACK_LOOP_SIZE) {
	debug_assert_eq!(0, (ptr as usize) % USIZE_BYTES);

	let a = (ptr as const usize);
	let b = (ptr_add(ptr, USIZE_BYTES) as const usize);
	if (a \| b) & ASCII_MASK != 0 {
	// What a kludge. We wrap the position finding code into
	// a non-inlineable function, which makes the codegen in
	// the tight loop above a bit better by avoiding a
	// couple extra movs. We pay for it by two additional
	// stores, but only in the case of finding a non-ASCII
	// byte.
	#[inline(never)]
	unsafe fn findpos(
	start_ptr: *const u8,
	ptr: *const u8,
	) -> usize {
	let a = (ptr as const usize);
	let b = (ptr_add(ptr, USIZE_BYTES) as const usize);

	let mut at = sub(ptr, start_ptr);
	let maska = a & ASCII_MASK;
	if maska != 0 {
	return at + first_non_ascii_byte_mask(maska);
	}

	at += USIZE_BYTES;
	let maskb = b & ASCII_MASK;
	debug_assert!(maskb != 0);
	return at + first_non_ascii_byte_mask(maskb);
	}
	return findpos(start_ptr, ptr);
	}
	ptr = ptr_add(ptr, FALLBACK_LOOP_SIZE);
	}
	}
	first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
	}
	}

	#[cfg(all(not(miri), target_arch = "x86_64"))]
	fn first_non_ascii_byte_sse2(slice: &[u8]) -> usize {
	use core::arch::x86_64::*;

	const VECTOR_SIZE: usize = core::mem::size_of::<__m128i>();
	const VECTOR_ALIGN: usize = VECTOR_SIZE - 1;
	const VECTOR_LOOP_SIZE: usize = 4 * VECTOR_SIZE;

	let start_ptr = slice.as_ptr();
	let end_ptr = slice[slice.len()..].as_ptr();
	let mut ptr = start_ptr;

	unsafe {
	if slice.len() < VECTOR_SIZE {
	return first_non_ascii_byte_slow(start_ptr, end_ptr, ptr);
	}

	let chunk = _mm_loadu_si128(ptr as *const __m128i);
	let mask = _mm_movemask_epi8(chunk);
	if mask != 0 {
	return mask.trailing_zeros() as usize;
	}

	ptr = ptr.add(VECTOR_SIZE - (start_ptr as usize & VECTOR_ALIGN));
	debug_assert!(ptr > start_ptr);
	debug_assert!(end_ptr.sub(VECTOR_SIZE) >= start_ptr);
	if slice.len() >= VECTOR_LOOP_SIZE {
	while ptr <= ptr_sub(end_ptr, VECTOR_LOOP_SIZE) {
	debug_assert_eq!(0, (ptr as usize) % VECTOR_SIZE);

	let a = _mm_load_si128(ptr as *const __m128i);
	let b = _mm_load_si128(ptr.add(VECTOR_SIZE) as *const __m128i);
	let c =
	_mm_load_si128(ptr.add(2 * VECTOR_SIZE) as *const __m128i);
	let d =
	_mm_load_si128(ptr.add(3 * VECTOR_SIZE) as *const __m128i);

	let or1 = _mm_or_si128(a, b);
	let or2 = _mm_or_si128(c, d);
	let or3 = _mm_or_si128(or1, or2);
	if _mm_movemask_epi8(or3) != 0 {
	let mut at = sub(ptr, start_ptr);
	let mask = _mm_movemask_epi8(a);
	if mask != 0 {
	return at + mask.trailing_zeros() as usize;
	}

	at += VECTOR_SIZE;
	let mask = _mm_movemask_epi8(b);
	if mask != 0 {
	return at + mask.trailing_zeros() as usize;
	}

	at += VECTOR_SIZE;
	let mask = _mm_movemask_epi8(c);
	if mask != 0 {
	return at + mask.trailing_zeros() as usize;
	}

	at += VECTOR_SIZE;
	let mask = _mm_movemask_epi8(d);
	debug_assert!(mask != 0);
	return at + mask.trailing_zeros() as usize;
	}
	ptr = ptr_add(ptr, VECTOR_LOOP_SIZE);
	}
	}
	while ptr <= end_ptr.sub(VECTOR_SIZE) {
	debug_assert!(sub(end_ptr, ptr) >= VECTOR_SIZE);

	let chunk = _mm_loadu_si128(ptr as *const __m128i);
	let mask = _mm_movemask_epi8(chunk);
	if mask != 0 {
	return sub(ptr, start_ptr) + mask.trailing_zeros() as usize;
	}
	ptr = ptr.add(VECTOR_SIZE);
	}
	first_non_ascii_byte_slow(start_ptr, end_ptr, ptr)
	}
	}

	#[inline(always)]
	unsafe fn first_non_ascii_byte_slow(
	start_ptr: *const u8,
	end_ptr: *const u8,
	mut ptr: *const u8,
	) -> usize {
	debug_assert!(start_ptr <= ptr);
	debug_assert!(ptr <= end_ptr);

	while ptr < end_ptr {
	if *ptr > 0x7F {
	return sub(ptr, start_ptr);
	}
	ptr = ptr.offset(1);
	}
	sub(end_ptr, start_ptr)
	}

	/// Compute the position of the first ASCII byte in the given mask.
	///
	/// The mask should be computed by `chunk & ASCII_MASK`, where `chunk` is
	/// 8 contiguous bytes of the slice being checked where at least one of those
	/// bytes is not an ASCII byte.
	///
	/// The position returned is always in the inclusive range [0, 7].
	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	fn first_non_ascii_byte_mask(mask: usize) -> usize {
	#[cfg(target_endian = "little")]
	{
	mask.trailing_zeros() as usize / 8
	}
	#[cfg(target_endian = "big")]
	{
	mask.leading_zeros() as usize / 8
	}
	}

	/// Increment the given pointer by the given amount.
	unsafe fn ptr_add(ptr: const u8, amt: usize) -> const u8 {
	debug_assert!(amt < ::core::isize::MAX as usize);
	ptr.offset(amt as isize)
	}

	/// Decrement the given pointer by the given amount.
	unsafe fn ptr_sub(ptr: const u8, amt: usize) -> const u8 {
	debug_assert!(amt < ::core::isize::MAX as usize);
	ptr.offset((amt as isize).wrapping_neg())
	}

	#[cfg(any(test, miri, not(target_arch = "x86_64")))]
	unsafe fn read_unaligned_usize(ptr: *const u8) -> usize {
	use core::ptr;

	let mut n: usize = 0;
	ptr::copy_nonoverlapping(ptr, &mut n as mut _ as mut u8, USIZE_BYTES);
	n
	}

	/// Subtract `b` from `a` and return the difference. `a` should be greater than
	/// or equal to `b`.
	fn sub(a: const u8, b: const u8) -> usize {
	debug_assert!(a >= b);
	(a as usize) - (b as usize)
	}

	#[cfg(test)]
	mod tests {
	use super::*;

	// Our testing approach here is to try and exhaustively test every case.
	// This includes the position at which a non-ASCII byte occurs in addition
	// to the alignment of the slice that we're searching.

	#[test]
	fn positive_fallback_forward() {
	for i in 0..517 {
	let s = "a".repeat(i);
	assert_eq!(
	i,
	first_non_ascii_byte_fallback(s.as_bytes()),
	"i: {:?}, len: {:?}, s: {:?}",
	i,
	s.len(),
	s
	);
	}
	}

	#[test]
	#[cfg(target_arch = "x86_64")]
	#[cfg(not(miri))]
	fn positive_sse2_forward() {
	for i in 0..517 {
	let b = "a".repeat(i).into_bytes();
	assert_eq!(b.len(), first_non_ascii_byte_sse2(&b));
	}
	}

	#[test]
	#[cfg(not(miri))]
	fn negative_fallback_forward() {
	for i in 0..517 {
	for align in 0..65 {
	let mut s = "a".repeat(i);
	s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
	let s = s.get(align..).unwrap_or("");
	assert_eq!(
	i.saturating_sub(align),
	first_non_ascii_byte_fallback(s.as_bytes()),
	"i: {:?}, align: {:?}, len: {:?}, s: {:?}",
	i,
	align,
	s.len(),
	s
	);
	}
	}
	}

	#[test]
	#[cfg(target_arch = "x86_64")]
	#[cfg(not(miri))]
	fn negative_sse2_forward() {
	for i in 0..517 {
	for align in 0..65 {
	let mut s = "a".repeat(i);
	s.push_str("☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃☃");
	let s = s.get(align..).unwrap_or("");
	assert_eq!(
	i.saturating_sub(align),
	first_non_ascii_byte_sse2(s.as_bytes()),
	"i: {:?}, align: {:?}, len: {:?}, s: {:?}",
	i,
	align,
	s.len(),
	s
	);
	}
	}
	}
	}