guile-examples/sound/riff-wave/bytevector-utils.scm

(library (bytevector-utils)
  (export ascii-string->bytevector
          integer->bytevector)
  (import (except (rnrs base) let-values vector-for-each)
          (only (guile)
                lambda* λ)
          (rnrs bytevectors))


  (define ascii-string->bytevector
    (lambda* (string len #:key (endianness 'big))
      "Assuming, that string contains only ASCII characters."
      (cond
       [(eq? endianness 'big)
        (string->utf8 string)]
       [else
        (let ([bv (make-bytevector len 0)])
          (let iter
              ([index 0]
               [°char-nums (map char->integer (string->list string))])
            (cond
             [(null? °char-nums) bv]
             [else
              (bytevector-uint-set! bv
                                    (- (- len 1) index)
                                    (car °char-nums)
                                    endianness
                                    1)
              (iter (+ index 1) (cdr °char-nums))])))])))


  (define integer->bytevector
    (lambda* (int num-bytes #:key (endianness 'big) (index 0) (signed #t))
      (let ([bv (make-bytevector num-bytes)])
        (cond
         [signed
          (bytevector-sint-set! bv 0 int endianness num-bytes)]
         [else
          (bytevector-uint-set! bv 0 int endianness num-bytes)])
        bv))))



;; syntax:

;; SRFI-4: https://www.gnu.org/software/guile/manual/html_node/SRFI_002d4.html
;; BYTEVECTORS: https://www.gnu.org/software/guile/manual/html_node/Bytevectors.html

;; bitvector: #*1111000, (bitvector->list #*101010101010) -> (#t #f #t #f #t #f #t #f #t #f #t #f)
;; bytevector: #vu8(0-255 0-255 ...)

;; vector: #(1 2 3)
;; vector of hexadecimal digits -> integer: #xdeadbeef

;; other uniform number vectors:
;; https://www.gnu.org/software/guile/manual/html_node/SRFI_002d4-Overview.html

;; #s8(-10 1 3)
;; #s16(-10 1 3)
;; #s32(-10 1 3)
;; ...

;; equality:
;; (equal? #vu8(1 2 3) #u8(1 2 3))
;; (eqv? #vu8(1 2 3) #u8(1 2 3))
;; (eq? #vu8(1 2 3) #u8(1 2 3))

;; Big-endian means storing the most significant byte FIRST, not LAST, as the name would seem to suggest.
;; Little-endian means storing the least significant byte FIRST, not LAST, as the name would seem to suggest.