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; Part of Scheme 48 1.9. See file COPYING for notices and license.
; Authors: Harald Glab-Phlak, Mike Sperber
; R6RS bitwise operations
; Taken from the R6RS document.
(define (bitwise-if ei1 ei2 ei3)
(bitwise-ior (bitwise-and ei1 ei2)
(bitwise-and (bitwise-not ei1) ei3)))
(define bitwise-arithmetic-shift arithmetic-shift)
(define bitwise-arithmetic-shift-left bitwise-arithmetic-shift)
(define (bitwise-arithmetic-shift-right ei1 ei2)
(bitwise-arithmetic-shift ei1 (- ei2)))
(define bitwise-bit-count bit-count)
(define (bitwise-bit-set? ei1 ei2)
(not (zero?
(bitwise-and
(bitwise-arithmetic-shift-left 1 ei2)
ei1))))
(define (bitwise-bit-field ei1 ei2 ei3)
(let ((mask
(bitwise-not
(bitwise-arithmetic-shift-left -1 ei3))))
(bitwise-arithmetic-shift-right
(bitwise-and ei1 mask)
ei2)))
(define (bitwise-copy-bit ei1 ei2 ei3)
(bitwise-if (bitwise-arithmetic-shift-left 1 ei2)
(bitwise-arithmetic-shift-left ei3 ei2)
ei1))
(define (bitwise-copy-bit-field ei1 ei2 ei3 ei4)
(bitwise-if (bitwise-and (bitwise-arithmetic-shift-left -1 ei2)
(bitwise-not
(bitwise-arithmetic-shift-left -1 ei3)))
(bitwise-arithmetic-shift-left ei4 ei2)
ei1))
(define (bitwise-rotate-bit-field ei1 ei2 ei3 ei4)
(let* ((n ei1)
(start ei2)
(end ei3)
(count ei4)
(width (- end start)))
(if (positive? width)
(let* ((count (remainder count width))
(field0
(bitwise-bit-field n start end))
(field1 (bitwise-arithmetic-shift-left
field0 count))
(field2 (bitwise-arithmetic-shift-right
field0
(- width count)))
(field (bitwise-ior field1 field2)))
(bitwise-copy-bit-field n start end field))
n)))
(define (bitwise-reverse-bit-field ei1 ei2 ei3)
(letrec* ((reverse-bit-field-recur
(lambda (n1 n2 len)
(if (> len 0)
(reverse-bit-field-recur
(bitwise-arithmetic-shift-right n1 1)
(bitwise-copy-bit (bitwise-arithmetic-shift-left n2 1) 0 n1)
(- len 1))
n2))))
(let ((width (- ei3 ei2)))
(if (positive? width)
(let ((field (bitwise-bit-field ei1 ei2 ei3)))
(bitwise-copy-bit-field
ei1 ei2 ei3 (reverse-bit-field-recur field 0 width)))
ei1))))
(define (bitwise-length ei)
(do ((result 0 (+ result 1))
(bits (if (negative? ei)
(bitwise-not ei)
ei)
(bitwise-arithmetic-shift bits -1)))
((zero? bits)
result)))
(define (bitwise-first-bit-set ei)
(cond ((eq? ei 0) -1)
((eq? (remainder ei 2) 1) 0)
((eq? (remainder ei 2) 0)
(let loop ((num ei)
(count 0))
(if (or (eq? num 1)
(eq? (remainder num 2) 1))
count
(loop (bitwise-arithmetic-shift-right num 1) (+ count 1)))))))
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