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silk.num.u8.

Eight-bit unsigned integers for bytes, compact counters, and exact binary representations.

When to use#

Use u8 for an individual byte or a field specified as eight unsigned bits. Prefer a wider integer for general counting unless the 0 through 255 range is intentional.

Details#

Each arithmetic operation has four forms with different overflow rules:

  • The plain form, such as add, traps on overflow. Use it when overflow is a program error.

  • The checked form, such as checkedAdd, returns None on overflow. Use it when input data controls the operands.

  • The wrapping form, such as wrappingAdd, computes the result modulo 2^8.

  • The saturating form, such as saturatingAdd, returns MIN or MAX on overflow.

Division and remainder by zero trap. checkedDivide and checkedRemainder return None. The shift count must be in the range 0 to BITS - 1. Otherwise, the program traps. A rotate reduces its count modulo BITS, so each count is valid. A right shift inserts zero bits.

A to conversion, such as toU8, traps if the value is out of the range of the destination type. A checkedTo conversion returns None instead. Conversion to f32 or f64 is exact.

A wrappingTo conversion, such as wrappingToI16, never traps. It keeps the low bits of the two's complement form of the value, like a cast in C or Rust, so it truncates, sign-extends, or reinterprets bits.

countOnes, leadingZeros, and trailingZeros count the bits of the value. For zero, both zero counts return BITS.

parse reads decimal text. A sign is not valid. To write a value as text, use silk.text.format.Format.display or Format.displayWith with a Writer. Neither needs an Allocator.

Examples#

Choose an overflow policy instead of relying on a trap#

silk
import silk.core.option { Option }
import silk.num.u8

pub fn main() -> i32 {
  let checked = u8.checkedAdd(255, 1)
  let recovered = move checked |> Option<u8>.unwrapOr(42)
  if recovered != 42 {
    return 1
  }
  if u8.wrappingAdd(255, 1) != 0 {
    return 1
  }
  if u8.saturatingAdd(255, 1) != 255 {
    return 1
  }
  return 0
}

Parse decimal text and reject invalid text#

silk
import silk.text.format { ParseError }
import silk.core.result { Result }
import silk.num.u8

pub fn main() -> i32 {
  let parsed = u8.parse("42") |> Result<u8, ParseError>.unwrapOr(0)
  let invalid = u8.parse("4x2") |> Result<u8, ParseError>.unwrapOr(0)
  if parsed != 42 || invalid != 0 {
    return 1
  }
  return 0
}

See also#

Use the silk.text.char module when a value is a Unicode scalar rather than an arbitrary byte.

Import as u8 with import silk.num.u8.

Public declarations: 70.

MAX#

silk
pub const MAX: u8

The largest u8 value.

MIN#

silk
pub const MIN: u8

The smallest u8 value.

BITS#

silk
pub const BITS: u32

The fixed width of u8, in bits.

toU8#

silk
pub fn toU8(value: u8) -> u8

Returns value unchanged as u8. Use this function when generic conversion code can select u8 as both source and destination.

checkedToU8#

silk
pub fn checkedToU8(value: u8) -> Option<u8>

Returns Some with value unchanged as u8. Use this function when generic checked-conversion code can select the same source and destination type.

toU16#

silk
pub fn toU16(value: u8) -> u16

Converts value exactly to u16. Every u8 value is representable.

checkedToU16#

silk
pub fn checkedToU16(value: u8) -> Option<u16>

Converts value exactly to u16 and returns Some. Every u8 value is representable.

toU32#

silk
pub fn toU32(value: u8) -> u32

Converts value exactly to u32. Every u8 value is representable.

checkedToU32#

silk
pub fn checkedToU32(value: u8) -> Option<u32>

Converts value exactly to u32 and returns Some. Every u8 value is representable.

toU64#

silk
pub fn toU64(value: u8) -> u64

Converts value exactly to u64. Every u8 value is representable.

checkedToU64#

silk
pub fn checkedToU64(value: u8) -> Option<u64>

Converts value exactly to u64 and returns Some. Every u8 value is representable.

toUsize#

silk
pub fn toUsize(value: u8) -> usize

Converts value exactly to usize. Every u8 value is representable.

checkedToUsize#

silk
pub fn checkedToUsize(value: u8) -> Option<usize>

Converts value exactly to usize and returns Some. Every u8 value is representable.

toI8#

silk
pub fn toI8(value: u8) -> i8

Converts value to i8. Traps if value is outside the i8 range. Use this function when an out-of-range value is a program error.

checkedToI8#

silk
pub fn checkedToI8(value: u8) -> Option<i8>

Converts value to i8, or returns None if value is outside the i8 range. Use this function when an out-of-range value is input data.

toI16#

silk
pub fn toI16(value: u8) -> i16

Converts value exactly to i16. Every u8 value is representable.

checkedToI16#

silk
pub fn checkedToI16(value: u8) -> Option<i16>

Converts value exactly to i16 and returns Some. Every u8 value is representable.

toI32#

silk
pub fn toI32(value: u8) -> i32

Converts value exactly to i32. Every u8 value is representable.

checkedToI32#

silk
pub fn checkedToI32(value: u8) -> Option<i32>

Converts value exactly to i32 and returns Some. Every u8 value is representable.

toI64#

silk
pub fn toI64(value: u8) -> i64

Converts value exactly to i64. Every u8 value is representable.

checkedToI64#

silk
pub fn checkedToI64(value: u8) -> Option<i64>

Converts value exactly to i64 and returns Some. Every u8 value is representable.

toIsize#

silk
pub fn toIsize(value: u8) -> isize

Converts value exactly to isize. Every u8 value is representable.

checkedToIsize#

silk
pub fn checkedToIsize(value: u8) -> Option<isize>

Converts value exactly to isize and returns Some. Every u8 value is representable.

toF32#

silk
pub fn toF32(value: u8) -> f32

Converts value exactly to f32. Every u8 value is below 2^24 and so is exactly representable.

toF64#

silk
pub fn toF64(value: u8) -> f64

Converts value exactly to f64. Every u8 value is below 2^53 and so is exactly representable.

wrappingToU8#

silk
pub fn wrappingToU8(value: u8) -> u8

Returns value unchanged. Use this function when generic wrapping-conversion code can select u8 as both source and destination.

wrappingToU16#

silk
pub fn wrappingToU16(value: u8) -> u16

Converts value to u16 modulo 2^16. Keeps the low 16 bits of the two's complement form of value and reads them as u16, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToU32#

silk
pub fn wrappingToU32(value: u8) -> u32

Converts value to u32 modulo 2^32. Keeps the low 32 bits of the two's complement form of value and reads them as u32, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToU64#

silk
pub fn wrappingToU64(value: u8) -> u64

Converts value to u64 modulo 2^64. Keeps the low 64 bits of the two's complement form of value and reads them as u64, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToUsize#

silk
pub fn wrappingToUsize(value: u8) -> usize

Converts value to usize modulo 2^usize.BITS. Keeps the low usize.BITS bits of the two's complement form of value and reads them as usize, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToI8#

silk
pub fn wrappingToI8(value: u8) -> i8

Converts value to i8 modulo 2^8. Keeps the low 8 bits of the two's complement form of value and reads them as i8, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToI16#

silk
pub fn wrappingToI16(value: u8) -> i16

Converts value to i16 modulo 2^16. Keeps the low 16 bits of the two's complement form of value and reads them as i16, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToI32#

silk
pub fn wrappingToI32(value: u8) -> i32

Converts value to i32 modulo 2^32. Keeps the low 32 bits of the two's complement form of value and reads them as i32, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToI64#

silk
pub fn wrappingToI64(value: u8) -> i64

Converts value to i64 modulo 2^64. Keeps the low 64 bits of the two's complement form of value and reads them as i64, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

wrappingToIsize#

silk
pub fn wrappingToIsize(value: u8) -> isize

Converts value to isize modulo 2^isize.BITS. Keeps the low isize.BITS bits of the two's complement form of value and reads them as isize, so it never traps. Use this function for deliberate truncation, sign extension, or bit reinterpretation, such as reading a signed field.

add#

silk
pub fn add(left: u8, right: u8) -> u8

Returns left + right and traps if the result is outside the u8 range. Use this function when overflow is a program error.

subtract#

silk
pub fn subtract(left: u8, right: u8) -> u8

Returns left - right and traps if the result is outside the u8 range. Use this function when overflow is a program error.

multiply#

silk
pub fn multiply(left: u8, right: u8) -> u8

Returns left * right and traps if the result is outside the u8 range. Use this function when overflow is a program error.

divide#

silk
pub fn divide(left: u8, right: u8) -> u8

Returns left / right. Traps if right is zero. Use this function when a zero divisor is a program error.

remainder#

silk
pub fn remainder(left: u8, right: u8) -> u8

Returns the remainder of left / right. Traps if right is zero. Use this function when a zero divisor is a program error.

bitAnd#

silk
pub fn bitAnd(left: u8, right: u8) -> u8

Returns the bitwise AND of left and right.

bitOr#

silk
pub fn bitOr(left: u8, right: u8) -> u8

Returns the bitwise OR of left and right.

bitXor#

silk
pub fn bitXor(left: u8, right: u8) -> u8

Returns the bitwise exclusive OR of left and right.

bitNot#

silk
pub fn bitNot(value: u8) -> u8

Returns value with each bit inverted.

shiftLeft#

silk
pub fn shiftLeft(left: u8, right: u8) -> u8

Shifts left bits left by right positions. Traps if right is not less than BITS.

shiftRight#

silk
pub fn shiftRight(left: u8, right: u8) -> u8

Shifts left bits right by right positions and inserts zero bits. Traps if right is not less than BITS.

rotateLeft#

silk
pub fn rotateLeft(left: u8, right: u8) -> u8

Rotates the bits of left left by right positions. The count is reduced modulo BITS, so each count is valid.

rotateRight#

silk
pub fn rotateRight(left: u8, right: u8) -> u8

Rotates the bits of left right by right positions. The count is reduced modulo BITS, so each count is valid.

countOnes#

silk
pub fn countOnes(value: u8) -> u32

Returns the number of one bits in value.

leadingZeros#

silk
pub fn leadingZeros(value: u8) -> u32

Returns the number of zero bits above the highest one bit of value. Returns BITS for zero.

trailingZeros#

silk
pub fn trailingZeros(value: u8) -> u32

Returns the number of zero bits below the lowest one bit of value. Returns BITS for zero.

wrappingAdd#

silk
pub fn wrappingAdd(left: u8, right: u8) -> u8

Returns left + right, wrapped to the u8 range. Use this function for deliberate modulo arithmetic.

wrappingSubtract#

silk
pub fn wrappingSubtract(left: u8, right: u8) -> u8

Returns left - right, wrapped to the u8 range. Use this function for deliberate modulo arithmetic.

wrappingMultiply#

silk
pub fn wrappingMultiply(left: u8, right: u8) -> u8

Returns left * right, wrapped to the u8 range. Use this function for deliberate modulo arithmetic.

saturatingAdd#

silk
pub fn saturatingAdd(left: u8, right: u8) -> u8

Returns left + right, clamped to MIN or MAX. Use this function when a boundary value is the required overflow result.

saturatingSubtract#

silk
pub fn saturatingSubtract(left: u8, right: u8) -> u8

Returns left - right, clamped to MIN or MAX. Use this function when a boundary value is the required overflow result.

saturatingMultiply#

silk
pub fn saturatingMultiply(left: u8, right: u8) -> u8

Returns left * right, clamped to MIN or MAX. Use this function when a boundary value is the required overflow result.

multiplyHigh#

silk
pub fn multiplyHigh(left: u8, right: u8) -> u8

Returns the high 8 bits of the exact 16-bit product left * right. It never overflows.

When to use#

Use this function with wrappingMultiply, which returns the low 8 bits, when an algorithm needs the full product, such as multi-word arithmetic, multiply-shift hashing, or division by a precomputed reciprocal.

checkedAdd#

silk
pub fn checkedAdd(left: u8, right: u8) -> Option<u8>

Returns Some with left + right, or None if the result is outside the u8 range. Use this function when overflow is input data.

checkedSubtract#

silk
pub fn checkedSubtract(left: u8, right: u8) -> Option<u8>

Returns Some with left - right, or None if the result is outside the u8 range. Use this function when overflow is input data.

checkedMultiply#

silk
pub fn checkedMultiply(left: u8, right: u8) -> Option<u8>

Returns Some with left * right, or None if the result is outside the u8 range. Use this function when overflow is input data.

checkedDivide#

silk
pub fn checkedDivide(left: u8, right: u8) -> Option<u8>

Returns Some with left / right, or None if right is zero. Use this function when a zero divisor is input data.

checkedRemainder#

silk
pub fn checkedRemainder(left: u8, right: u8) -> Option<u8>

Returns Some with the remainder, or None if right is zero. Use this function when a zero divisor is input data.

equals#

silk
pub fn equals(left: u8, right: u8) -> bool

Returns true if left and right are equal.

notEquals#

silk
pub fn notEquals(left: u8, right: u8) -> bool

Returns true if left and right are not equal.

lessThan#

silk
pub fn lessThan(left: u8, right: u8) -> bool

Returns true if left is less than right.

lessOrEqual#

silk
pub fn lessOrEqual(left: u8, right: u8) -> bool

Returns true if left is less than or equal to right.

greaterThan#

silk
pub fn greaterThan(left: u8, right: u8) -> bool

Returns true if left is greater than right.

greaterOrEqual#

silk
pub fn greaterOrEqual(left: u8, right: u8) -> bool

Returns true if left is greater than or equal to right.

parse#

silk
pub fn parse(text: string) -> Result<u8, ParseError>

Returns the u8 value of the decimal text text, or a ParseError.

Details#

The complete text must be one decimal number. This function does not skip spaces and does not accept digit separators.

Errors#

  • ParseError with reason silk.text.format.NotANumber if text is empty, has a sign, contains a byte that is not a digit, or has bytes after the number. offset gives the byte position where the read stopped.

  • ParseError with reason silk.text.format.OutOfRange if the number is outside the range of u8.

Category: Numbers.

Profiles: aarch64-apple-darwin, aarch64-unknown-linux-gnu, aarch64-unknown-linux-gnu-no-libc, x86_64-unknown-linux-gnu, x86_64-unknown-linux-gnu-no-libc, wasm32-unknown-unknown, wasm32-wasip1, wasm32-wasip2.

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