Scheme Programmer's Manual

NAME

bytevector-s16-set!, bytevector-s32-set!, bytevector-s64-set!, bytevector-u16-set!, bytevector-u32-set!, bytevector-u64-set!, bytevector-ieee-double-set!, bytevector-ieee-single-set!, bytevector-s16-native-set!, bytevector-s32-native-set!, bytevector-s64-native-set!, bytevector-u16-native-set!, bytevector-u32-native-set!, bytevector-u64-native-set!, bytevector-ieee-double-native-set!, bytevector-ieee-single-native-set! - store a number in a bytevector

LIBRARY

(import (rnrs))                     ;R6RS
(import (rnrs bytevectors))         ;R6RS

SYNOPSIS

(bytevector-s16-set! bytevector k n endianness)
(bytevector-s32-set! bytevector k n endianness)
(bytevector-s64-set! bytevector k n endianness)

(bytevector-u16-set! bytevector k n endianness)
(bytevector-u32-set! bytevector k n endianness)
(bytevector-u64-set! bytevector k n endianness)

(bytevector-ieee-double-set! bytevector k x endianness)
(bytevector-ieee-single-set! bytevector k x endianness)

(bytevector-s16-native-set! bytevector k n)
(bytevector-s32-native-set! bytevector k n)
(bytevector-s64-native-set! bytevector k n)

(bytevector-u16-native-set! bytevector k n)
(bytevector-u32-native-set! bytevector k n)
(bytevector-u64-native-set! bytevector k n)

(bytevector-ieee-double-native-set! bytevector k x)
(bytevector-ieee-single-native-set! bytevector k x)

DESCRIPTION

Store the integer n or the real x in bytevector, starting from the index k. The byte representation is created according to a data type and endianness. The data type is one of the following:

s16: signed 16-bit integer
s32: signed 32-bit integer
s64: signed 64-bit integer
u16: unsigned 16-bit integer
u32: unsigned 32-bit integer
u64: unsigned 64-bit integer
ieee-double: IEEE-754 double-precision float (binary64)
ieee-single: IEEE-754 single-precision float (binary32)

The signed variants use the two's complement representation.

The endianness is normally one of the following symbols:

big: Big endian. The more significant bytes come before the less significant bytes.
little: Little endian. The less significant bytes come before the more significant bytes.

The -native variants use the machine's native endianness and furthermore impose an alignment requirement: the index k must be evenly divisible by the data type size (2, 4 or 8). Such an access is said to be aligned, as opposed to an unaligned access.

The number of bytes m used depends on the data type and is either two, four or eight (corresponding to 16, 32 or 64 bits). The bytevector must be at least k+m bytes in length.

The integer n must be in the range [0, (2^w)-1] for the unsigned operations and in the range [-(2^(w-1)), (2^(w-1))-1] for the signed operations, where w is the size of the data type in bits. For the floating point operations, x must be a real number object.

Unlike the equivalent operation in e.g. C, the index is not multiplied by the element size.

RETURN VALUES

Returns unspecified values.

EXAMPLES

(define b
  (u8-list->bytevector
    '(255 255 255 255 255 255 255 255
      255 255 255 255 255 255 255 253)))

(bytevector-u16-set! b 0 12345 (endianness little)) (bytevector-u16-ref b 0 (endianness little))
=> 12345

(bytevector-u16-native-set! b 0 12345) (bytevector-u16-native-ref b 0)
=> 12345 (bytevector-u16-ref b 0 (endianness little))
=> unspecified

COMPATIBILITY

See the notes in bytevector-u16-ref(3).

ERRORS

This procedure can raise exceptions with the following condition types:

&assertion (R6RS): The wrong number of arguments was passed or an argument was outside its domain.
R7RS: The assertions described above are errors. Implementations may signal an error, extend the procedure's domain of definition to include such arguments, or fail catastrophically.

STANDARDS

R6RS

AUTHORS

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