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### 7.5.30 SRFI-60 - Integers as Bits

This SRFI provides various functions for treating integers as bits and for bitwise manipulations. These functions can be obtained with,

(use-modules (srfi srfi-60))

Integers are treated as infinite precision twos-complement, the same as in the core logical functions (see section Bitwise Operations). And likewise bit indexes start from 0 for the least significant bit. The following functions in this SRFI are already in the Guile core,

`logand`

,`logior`

,`logxor`

,`lognot`

,`logtest`

,`logcount`

,`integer-length`

,`logbit?`

,`ash`

- Function:
**bitwise-and***n1 ...* - Function:
**bitwise-ior***n1 ...* - Function:
**bitwise-xor***n1 ...* - Function:
**bitwise-not***n* - Function:
**any-bits-set?***j k* - Function:
**bit-set?***index n* - Function:
**arithmetic-shift***n count* - Function:
**bit-field***n start end* - Function:
**bit-count***n* Aliases for

`logand`

,`logior`

,`logxor`

,`lognot`

,`logtest`

,`logbit?`

,`ash`

,`bit-extract`

and`logcount`

respectively.Note that the name

`bit-count`

conflicts with`bit-count`

in the core (see section Bit Vectors).

- Function:
**bitwise-if***mask n1 n0* - Function:
**bitwise-merge***mask n1 n0* Return an integer with bits selected from

`n1`and`n0`according to`mask`. Those bits where`mask`has 1s are taken from`n1`, and those where`mask`has 0s are taken from`n0`.(bitwise-if 3 #b0101 #b1010) ⇒ 9

- Function:
**log2-binary-factors***n* - Function:
**first-set-bit***n* Return a count of how many factors of 2 are present in

`n`. This is also the bit index of the lowest 1 bit in`n`. If`n`is 0, the return is*-1*.(log2-binary-factors 6) ⇒ 1 (log2-binary-factors -8) ⇒ 3

- Function:
**copy-bit***index n newbit* Return

`n`with the bit at`index`set according to`newbit`.`newbit`should be`#t`

to set the bit to 1, or`#f`

to set it to 0. Bits other than at`index`are unchanged in the return.(copy-bit 1 #b0101 #t) ⇒ 7

- Function:
**copy-bit-field***n newbits start end* Return

`n`with the bits from`start`(inclusive) to`end`(exclusive) changed to the value`newbits`.The least significant bit in

`newbits`goes to`start`, the next to, etc. Anything in`start`+1`newbits`past the`end`given is ignored.(copy-bit-field #b10000 #b11 1 3) ⇒ #b10110

- Function:
**rotate-bit-field***n count start end* Return

`n`with the bit field from`start`(inclusive) to`end`(exclusive) rotated upwards by`count`bits.`count`can be positive or negative, and it can be more than the field width (it’ll be reduced modulo the width).(rotate-bit-field #b0110 2 1 4) ⇒ #b1010

- Function:
**reverse-bit-field***n start end* Return

`n`with the bits from`start`(inclusive) to`end`(exclusive) reversed.(reverse-bit-field #b101001 2 4) ⇒ #b100101

- Function:
**integer->list***n [len]* Return bits from

`n`in the form of a list of`#t`

for 1 and`#f`

for 0. The least significant`len`bits are returned, and the first list element is the most significant of those bits. If`len`is not given, the default is`(integer-length`

(see section Bitwise Operations).`n`)(integer->list 6) ⇒ (#t #t #f) (integer->list 1 4) ⇒ (#f #f #f #t)

- Function:
**list->integer***lst* - Function:
**booleans->integer***bool…* Return an integer formed bitwise from the given

`lst`list of booleans, or for`booleans->integer`

from the`bool`arguments.Each boolean is

`#t`

for a 1 and`#f`

for a 0. The first element becomes the most significant bit in the return.(list->integer '(#t #f #t #f)) ⇒ 10

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