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GNU Emacs supports two numeric data types: *integers* and
*floating-point numbers*. Integers are whole numbers such as
-3, 0, 7, 13, and 511. Floating-point numbers are numbers with
fractional parts, such as -4.5, 0.0, and 2.71828. They can
also be expressed in exponential notation: ‘`1.5e2`’ is the same as
‘`150.0`’; here, ‘`e2`’ stands for ten to the second power, and
that is multiplied by 1.5. Integer computations are exact, though
they may overflow. Floating-point computations often involve rounding
errors, as the numbers have a fixed amount of precision.

1.1 Integer Basics | Representation and range of integers. | |

1.2 Floating-Point Basics | Representation and range of floating point. | |

1.3 Type Predicates for Numbers | Testing for numbers. | |

1.4 Comparison of Numbers | Equality and inequality predicates. | |

1.5 Numeric Conversions | Converting float to integer and vice versa. | |

1.6 Arithmetic Operations | How to add, subtract, multiply and divide. | |

1.7 Rounding Operations | Explicitly rounding floating-point numbers. | |

1.8 Bitwise Operations on Integers | Logical and, or, not, shifting. | |

1.9 Standard Mathematical Functions | Trig, exponential and logarithmic functions. | |

1.10 Random Numbers | Obtaining random integers, predictable or not. |

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The range of values for an integer depends on the machine. The minimum range is -536,870,912 to 536,870,911 (30 bits; i.e., -2**29 to 2**29 - 1), but many machines provide a wider range. Many examples in this chapter assume the minimum integer width of 30 bits.

The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period. An integer that is out of the Emacs range is treated as a floating-point number.

1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer -1. 9000000000000000000 ; The floating-point number 9e18. 0 ; The integer 0. -0 ; The integer 0.

The syntax for integers in bases other than 10 uses ‘`#`’
followed by a letter that specifies the radix: ‘`b`’ for binary,
‘`o`’ for octal, ‘`x`’ for hex, or ‘` radixr`’ to
specify radix

#b101100 ⇒ 44 #o54 ⇒ 44 #x2c ⇒ 44 #24r1k ⇒ 44

To understand how various functions work on integers, especially the bitwise operators (see section Bitwise Operations on Integers), it is often helpful to view the numbers in their binary form.

In 30-bit binary, the decimal integer 5 looks like this:

0000...000101 (30 bits total)

(The ‘`...`’ stands for enough bits to fill out a 30-bit word; in
this case, ‘`...`’ stands for twenty 0 bits. Later examples also
use the ‘`...`’ notation to make binary integers easier to read.)

The integer -1 looks like this:

1111...111111 (30 bits total)

-1 is represented as 30 ones. (This is called *two’s
complement* notation.)

Subtracting 4 from -1 returns the negative integer -5. In binary, the decimal integer 4 is 100. Consequently, -5 looks like this:

1111...111011 (30 bits total)

In this implementation, the largest 30-bit binary integer is 536,870,911 in decimal. In binary, it looks like this:

0111...111111 (30 bits total)

Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 536,870,911, the value is the negative integer -536,870,912:

(+ 1 536870911) ⇒ -536870912 ⇒ 1000...000000 (30 bits total)

Many of the functions described in this chapter accept markers for
arguments in place of numbers. (@xref{Markers}.) Since the actual
arguments to such functions may be either numbers or markers, we often
give these arguments the name `number-or-marker`. When the argument
value is a marker, its position value is used and its buffer is ignored.

- Variable:
**most-positive-fixnum** The value of this variable is the largest integer that Emacs Lisp can handle. Typical values are 2**29 - 1 on 32-bit and 2**61 - 1 on 64-bit platforms.

- Variable:
**most-negative-fixnum** The value of this variable is the smallest integer that Emacs Lisp can handle. It is negative. Typical values are -2**29 on 32-bit and -2**61 on 64-bit platforms.

In Emacs Lisp, text characters are represented by integers. Any
integer between zero and the value of `(max-char)`

, inclusive, is
considered to be valid as a character. @xref{Character Codes}.

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Floating-point numbers are useful for representing numbers that are
not integral. The range of floating-point numbers is
the same as the range of the C data type `double`

on the machine
you are using. On all computers currently supported by Emacs, this is
double-precision IEEE floating point.

The read syntax for floating-point numbers requires either a decimal
point, an exponent, or both. Optional signs (‘`+`’ or ‘`-`’)
precede the number and its exponent. For example, ‘`1500.0`’,
‘`+15e2`’, ‘`15.0e+2`’, ‘`+1500000e-3`’, and ‘`.15e4`’ are
five ways of writing a floating-point number whose value is 1500.
They are all equivalent. Like Common Lisp, Emacs Lisp requires at
least one digit after any decimal point in a floating-point number;
‘`1500.`’ is an integer, not a floating-point number.

Emacs Lisp treats `-0.0`

as numerically equal to ordinary zero
with respect to `equal`

and `=`

. This follows the
IEEE floating-point standard, which says `-0.0`

and
`0.0`

are numerically equal even though other operations can
distinguish them.

The IEEE floating-point standard supports positive
infinity and negative infinity as floating-point values. It also
provides for a class of values called NaN, or “not a number”;
numerical functions return such values in cases where there is no
correct answer. For example, `(/ 0.0 0.0)`

returns a NaN.
Although NaN values carry a sign, for practical purposes there is no other
significant difference between different NaN values in Emacs Lisp.

Here are read syntaxes for these special floating-point values:

- infinity
‘

`1.0e+INF`’ and ‘`-1.0e+INF`’- not-a-number
‘

`0.0e+NaN`’ and ‘`-0.0e+NaN`’

The following functions are specialized for handling floating-point numbers:

- Function:
**isnan***x* This predicate returns

`t`

if its floating-point argument is a NaN,`nil`

otherwise.

- Function:
**frexp***x* This function returns a cons cell

`(`

, where`s`.`e`)`s`and`e`are respectively the significand and exponent of the floating-point number`x`.If

`x`is finite, then`s`is a floating-point number between 0.5 (inclusive) and 1.0 (exclusive),`e`is an integer, and`x`=`s`* 2**`e`. If`x`is zero or infinity, then`s`is the same as`x`. If`x`is a NaN, then`s`is also a NaN. If`x`is zero, then`e`is 0.

- Function:
**ldexp***s e* Given a numeric significand

`s`and an integer exponent`e`, this function returns the floating point number`s`* 2**`e`.

- Function:
**copysign***x1 x2* This function copies the sign of

`x2`to the value of`x1`, and returns the result.`x1`and`x2`must be floating point.

- Function:
**logb***x* This function returns the binary exponent of

`x`. More precisely, the value is the logarithm base 2 of*|x|*, rounded down to an integer.(logb 10) ⇒ 3 (logb 10.0e20) ⇒ 69

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The functions in this section test for numbers, or for a specific
type of number. The functions `integerp`

and `floatp`

can
take any type of Lisp object as argument (they would not be of much
use otherwise), but the `zerop`

predicate requires a number as
its argument. See also `integer-or-marker-p`

and
`number-or-marker-p`

, in @ref{Predicates on Markers}.

- Function:
**floatp***object* This predicate tests whether its argument is floating point and returns

`t`

if so,`nil`

otherwise.

- Function:
**integerp***object* This predicate tests whether its argument is an integer, and returns

`t`

if so,`nil`

otherwise.

- Function:
**numberp***object* This predicate tests whether its argument is a number (either integer or floating point), and returns

`t`

if so,`nil`

otherwise.

- Function:
**natnump***object* -
This predicate (whose name comes from the phrase “natural number”) tests to see whether its argument is a nonnegative integer, and returns

`t`

if so,`nil`

otherwise. 0 is considered non-negative.`wholenump`

is a synonym for`natnump`

.

- Function:
**zerop***number* This predicate tests whether its argument is zero, and returns

`t`

if so,`nil`

otherwise. The argument must be a number.`(zerop x)`

is equivalent to`(= x 0)`

.

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To test numbers for numerical equality, you should normally use
`=`

, not `eq`

. There can be many distinct floating-point
objects with the same numeric value. If you use `eq`

to
compare them, then you test whether two values are the same
*object*. By contrast, `=`

compares only the numeric values
of the objects.

In Emacs Lisp, each integer is a unique Lisp object.
Therefore, `eq`

is equivalent to `=`

where integers are
concerned. It is sometimes convenient to use `eq`

for comparing
an unknown value with an integer, because `eq`

does not report an
error if the unknown value is not a number—it accepts arguments of
any type. By contrast, `=`

signals an error if the arguments are
not numbers or markers. However, it is better programming practice to
use `=`

if you can, even for comparing integers.

Sometimes it is useful to compare numbers with `equal`

, which
treats two numbers as equal if they have the same data type (both
integers, or both floating point) and the same value. By contrast,
`=`

can treat an integer and a floating-point number as equal.
@xref{Equality Predicates}.

There is another wrinkle: because floating-point arithmetic is not exact, it is often a bad idea to check for equality of floating-point values. Usually it is better to test for approximate equality. Here’s a function to do this:

(defvar fuzz-factor 1.0e-6) (defun approx-equal (x y) (or (= x y) (< (/ (abs (- x y)) (max (abs x) (abs y))) fuzz-factor)))

Common Lisp note:Comparing numbers in Common Lisp always requires`=`

because Common Lisp implements multi-word integers, and two distinct integer objects can have the same numeric value. Emacs Lisp can have just one integer object for any given value because it has a limited range of integers.

- Function:
**=***number-or-marker &rest number-or-markers* This function tests whether all its arguments are numerically equal, and returns

`t`

if so,`nil`

otherwise.

- Function:
**eql***value1 value2* This function acts like

`eq`

except when both arguments are numbers. It compares numbers by type and numeric value, so that`(eql 1.0 1)`

returns`nil`

, but`(eql 1.0 1.0)`

and`(eql 1 1)`

both return`t`

.

- Function:
**/=***number-or-marker1 number-or-marker2* This function tests whether its arguments are numerically equal, and returns

`t`

if they are not, and`nil`

if they are.

- Function:
**<***number-or-marker &rest number-or-markers* This function tests whether each argument is strictly less than the following argument. It returns

`t`

if so,`nil`

otherwise.

- Function:
**<=***number-or-marker &rest number-or-markers* This function tests whether each argument is less than or equal to the following argument. It returns

`t`

if so,`nil`

otherwise.

- Function:
**>***number-or-marker &rest number-or-markers* This function tests whether each argument is strictly greater than the following argument. It returns

`t`

if so,`nil`

otherwise.

- Function:
**>=***number-or-marker &rest number-or-markers* This function tests whether each argument is greater than or equal to the following argument. It returns

`t`

if so,`nil`

otherwise.

- Function:
**max***number-or-marker &rest numbers-or-markers* This function returns the largest of its arguments.

(max 20) ⇒ 20 (max 1 2.5) ⇒ 2.5 (max 1 3 2.5) ⇒ 3

- Function:
**min***number-or-marker &rest numbers-or-markers* This function returns the smallest of its arguments.

(min -4 1) ⇒ -4

- Function:
**abs***number* This function returns the absolute value of

`number`.

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To convert an integer to floating point, use the function `float`

.

- Function:
**float***number* This returns

`number`converted to floating point. If`number`is already floating point,`float`

returns it unchanged.

There are four functions to convert floating-point numbers to
integers; they differ in how they round. All accept an argument
`number` and an optional argument `divisor`. Both arguments
may be integers or floating-point numbers. `divisor` may also be
`nil`

. If `divisor` is `nil`

or omitted, these
functions convert `number` to an integer, or return it unchanged
if it already is an integer. If `divisor` is non-`nil`

, they
divide `number` by `divisor` and convert the result to an
integer. If `divisor` is zero (whether integer or
floating point), Emacs signals an `arith-error`

error.

- Function:
**truncate***number &optional divisor* This returns

`number`, converted to an integer by rounding towards zero.(truncate 1.2) ⇒ 1 (truncate 1.7) ⇒ 1 (truncate -1.2) ⇒ -1 (truncate -1.7) ⇒ -1

- Function:
**floor***number &optional divisor* This returns

`number`, converted to an integer by rounding downward (towards negative infinity).If

`divisor`is specified, this uses the kind of division operation that corresponds to`mod`

, rounding downward.(floor 1.2) ⇒ 1 (floor 1.7) ⇒ 1 (floor -1.2) ⇒ -2 (floor -1.7) ⇒ -2 (floor 5.99 3) ⇒ 1

- Function:
**ceiling***number &optional divisor* This returns

`number`, converted to an integer by rounding upward (towards positive infinity).(ceiling 1.2) ⇒ 2 (ceiling 1.7) ⇒ 2 (ceiling -1.2) ⇒ -1 (ceiling -1.7) ⇒ -1

- Function:
**round***number &optional divisor* This returns

`number`, converted to an integer by rounding towards the nearest integer. Rounding a value equidistant between two integers returns the even integer.(round 1.2) ⇒ 1 (round 1.7) ⇒ 2 (round -1.2) ⇒ -1 (round -1.7) ⇒ -2

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Emacs Lisp provides the traditional four arithmetic operations
(addition, subtraction, multiplication, and division), as well as
remainder and modulus functions, and functions to add or subtract 1.
Except for `%`

, each of these functions accepts both integer and
floating-point arguments, and returns a floating-point number if any
argument is floating point.

Emacs Lisp arithmetic functions do not check for integer overflow.
Thus `(1+ 536870911)`

may evaluate to
-536870912, depending on your hardware.

- Function:
**1+***number-or-marker* This function returns

`number-or-marker`plus 1. For example,(setq foo 4) ⇒ 4 (1+ foo) ⇒ 5

This function is not analogous to the C operator

`++`

—it does not increment a variable. It just computes a sum. Thus, if we continue,foo ⇒ 4

If you want to increment the variable, you must use

`setq`

, like this:(setq foo (1+ foo)) ⇒ 5

- Function:
**1-***number-or-marker* This function returns

`number-or-marker`minus 1.

- Function:
**+***&rest numbers-or-markers* This function adds its arguments together. When given no arguments,

`+`

returns 0.(+) ⇒ 0 (+ 1) ⇒ 1 (+ 1 2 3 4) ⇒ 10

- Function:
**-***&optional number-or-marker &rest more-numbers-or-markers* The

`-`

function serves two purposes: negation and subtraction. When`-`

has a single argument, the value is the negative of the argument. When there are multiple arguments,`-`

subtracts each of the`more-numbers-or-markers`from`number-or-marker`, cumulatively. If there are no arguments, the result is 0.(- 10 1 2 3 4) ⇒ 0 (- 10) ⇒ -10 (-) ⇒ 0

- Function:
******&rest numbers-or-markers* This function multiplies its arguments together, and returns the product. When given no arguments,

`*`

returns 1.(*) ⇒ 1 (* 1) ⇒ 1 (* 1 2 3 4) ⇒ 24

- Function:
**/***number &rest divisors* With one or more

`divisors`, this function divides`number`by each divisor in`divisors`in turn, and returns the quotient. With no`divisors`, this function returns 1/`number`, i.e., the multiplicative inverse of`number`. Each argument may be a number or a marker.If all the arguments are integers, the result is an integer, obtained by rounding the quotient towards zero after each division.

(/ 6 2) ⇒ 3

(/ 5 2) ⇒ 2

(/ 5.0 2) ⇒ 2.5

(/ 5 2.0) ⇒ 2.5

(/ 5.0 2.0) ⇒ 2.5

(/ 4.0) ⇒ 0.25

(/ 4) ⇒ 0

(/ 25 3 2) ⇒ 4

(/ -17 6) ⇒ -2

If you divide an integer by the integer 0, Emacs signals an

`arith-error`

error (@pxref{Errors}). Floating-point division of a nonzero number by zero yields either positive or negative infinity (see section Floating-Point Basics).

- Function:
**%***dividend divisor* -
This function returns the integer remainder after division of

`dividend`by`divisor`. The arguments must be integers or markers.For any two integers

`dividend`and`divisor`,(+ (%

`dividend``divisor`) (* (/`dividend``divisor`)`divisor`))always equals

`dividend`if`divisor`is nonzero.(% 9 4) ⇒ 1 (% -9 4) ⇒ -1 (% 9 -4) ⇒ 1 (% -9 -4) ⇒ -1

- Function:
**mod***dividend divisor* -
This function returns the value of

`dividend`modulo`divisor`; in other words, the remainder after division of`dividend`by`divisor`, but with the same sign as`divisor`. The arguments must be numbers or markers.Unlike

`%`

,`mod`

permits floating-point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder.If

`divisor`is zero,`mod`

signals an`arith-error`

error if both arguments are integers, and returns a NaN otherwise.(mod 9 4) ⇒ 1

(mod -9 4) ⇒ 3

(mod 9 -4) ⇒ -3

(mod -9 -4) ⇒ -1

(mod 5.5 2.5) ⇒ .5

For any two numbers

`dividend`and`divisor`,(+ (mod

`dividend``divisor`) (* (floor`dividend``divisor`)`divisor`))always equals

`dividend`, subject to rounding error if either argument is floating point and to an`arith-error`

if`dividend`is an integer and`divisor`is 0. For`floor`

, see Numeric Conversions.

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The functions `ffloor`

, `fceiling`

, `fround`

, and
`ftruncate`

take a floating-point argument and return a floating-point
result whose value is a nearby integer. `ffloor`

returns the
nearest integer below; `fceiling`

, the nearest integer above;
`ftruncate`

, the nearest integer in the direction towards zero;
`fround`

, the nearest integer.

- Function:
**ffloor***float* This function rounds

`float`to the next lower integral value, and returns that value as a floating-point number.

- Function:
**fceiling***float* This function rounds

`float`to the next higher integral value, and returns that value as a floating-point number.

- Function:
**ftruncate***float* This function rounds

`float`towards zero to an integral value, and returns that value as a floating-point number.

- Function:
**fround***float* This function rounds

`float`to the nearest integral value, and returns that value as a floating-point number. Rounding a value equidistant between two integers returns the even integer.

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In a computer, an integer is represented as a binary number, a
sequence of *bits* (digits which are either zero or one). A bitwise
operation acts on the individual bits of such a sequence. For example,
*shifting* moves the whole sequence left or right one or more places,
reproducing the same pattern moved over.

The bitwise operations in Emacs Lisp apply only to integers.

- Function:
**lsh***integer1 count* -
`lsh`

, which is an abbreviation for*logical shift*, shifts the bits in`integer1`to the left`count`places, or to the right if`count`is negative, bringing zeros into the vacated bits. If`count`is negative,`lsh`

shifts zeros into the leftmost (most-significant) bit, producing a positive result even if`integer1`is negative. Contrast this with`ash`

, below.Here are two examples of

`lsh`

, shifting a pattern of bits one place to the left. We show only the low-order eight bits of the binary pattern; the rest are all zero.(lsh 5 1) ⇒ 10 ;; Decimal 5 becomes decimal 10. 00000101 ⇒ 00001010 (lsh 7 1) ⇒ 14 ;; Decimal 7 becomes decimal 14. 00000111 ⇒ 00001110

As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.

Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):

`(lsh 3 2) ⇒ 12 ;; Decimal 3 becomes decimal 12. 00000011 ⇒ 00001100`

On the other hand, shifting one place to the right looks like this:

`(lsh 6 -1) ⇒ 3 ;; Decimal 6 becomes decimal 3. 00000110 ⇒ 00000011`

`(lsh 5 -1) ⇒ 2 ;; Decimal 5 becomes decimal 2. 00000101 ⇒ 00000010`

As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.

The function

`lsh`

, like all Emacs Lisp arithmetic functions, does not check for overflow, so shifting left can discard significant bits and change the sign of the number. For example, left shifting 536,870,911 produces -2 in the 30-bit implementation:`(lsh 536870911 1) ; left shift ⇒ -2`

In binary, the argument looks like this:

`;; Decimal 536,870,911 0111...111111 (30 bits total)`

which becomes the following when left shifted:

`;; Decimal -2 1111...111110 (30 bits total)`

- Function:
**ash***integer1 count* -
`ash`

(*arithmetic shift*) shifts the bits in`integer1`to the left`count`places, or to the right if`count`is negative.`ash`

gives the same results as`lsh`

except when`integer1`and`count`are both negative. In that case,`ash`

puts ones in the empty bit positions on the left, while`lsh`

puts zeros in those bit positions.Thus, with

`ash`

, shifting the pattern of bits one place to the right looks like this:`(ash -6 -1) ⇒ -3 ;; Decimal -6 becomes decimal -3. 1111...111010 (30 bits total) ⇒ 1111...111101 (30 bits total)`

In contrast, shifting the pattern of bits one place to the right with

`lsh`

looks like this:`(lsh -6 -1) ⇒ 536870909 ;; Decimal -6 becomes decimal 536,870,909. 1111...111010 (30 bits total) ⇒ 0111...111101 (30 bits total)`

Here are other examples:

; 30-bit binary values (lsh 5 2) ; 5 = 0000...000101 ⇒ 20 ; = 0000...010100

(ash 5 2) ⇒ 20 (lsh -5 2) ; -5 = 1111...111011 ⇒ -20 ; = 1111...101100 (ash -5 2) ⇒ -20

(lsh 5 -2) ; 5 = 0000...000101 ⇒ 1 ; = 0000...000001

(ash 5 -2) ⇒ 1

(lsh -5 -2) ; -5 = 1111...111011 ⇒ 268435454 ; = 0011...111110

(ash -5 -2) ; -5 = 1111...111011 ⇒ -2 ; = 1111...111110

- Function:
**logand***&rest ints-or-markers* This function returns the bitwise AND of the arguments: the

`n`th bit is 1 in the result if, and only if, the`n`th bit is 1 in all the arguments.For example, using 4-bit binary numbers, the bitwise AND of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are both 1 so the leftmost two bits of the returned value are both 1. However, for the rightmost two bits, each is 0 in at least one of the arguments, so the rightmost two bits of the returned value are both 0.

Therefore,

(logand 13 12) ⇒ 12

If

`logand`

is not passed any argument, it returns a value of -1. This number is an identity element for`logand`

because its binary representation consists entirely of ones. If`logand`

is passed just one argument, it returns that argument.; 30-bit binary values (logand 14 13) ; 14 = 0000...001110 ; 13 = 0000...001101 ⇒ 12 ; 12 = 0000...001100

(logand 14 13 4) ; 14 = 0000...001110 ; 13 = 0000...001101 ; 4 = 0000...000100 ⇒ 4 ; 4 = 0000...000100

`(logand) ⇒ -1 ; -1 = 1111...111111`

- Function:
**logior***&rest ints-or-markers* This function returns the bitwise inclusive OR of its arguments: the

`n`th bit is 1 in the result if, and only if, the`n`th bit is 1 in at least one of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If`logior`

is passed just one argument, it returns that argument.; 30-bit binary values (logior 12 5) ; 12 = 0000...001100 ; 5 = 0000...000101 ⇒ 13 ; 13 = 0000...001101

(logior 12 5 7) ; 12 = 0000...001100 ; 5 = 0000...000101 ; 7 = 0000...000111 ⇒ 15 ; 15 = 0000...001111

- Function:
**logxor***&rest ints-or-markers* This function returns the bitwise exclusive OR of its arguments: the

`n`th bit is 1 in the result if, and only if, the`n`th bit is 1 in an odd number of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If`logxor`

is passed just one argument, it returns that argument.; 30-bit binary values (logxor 12 5) ; 12 = 0000...001100 ; 5 = 0000...000101 ⇒ 9 ; 9 = 0000...001001

(logxor 12 5 7) ; 12 = 0000...001100 ; 5 = 0000...000101 ; 7 = 0000...000111 ⇒ 14 ; 14 = 0000...001110

- Function:
**lognot***integer* This function returns the bitwise complement of its argument: the

`n`th bit is one in the result if, and only if, the`n`th bit is zero in`integer`, and vice-versa.(lognot 5) ⇒ -6 ;; 5 = 0000...000101 (30 bits total) ;; becomes ;; -6 = 1111...111010 (30 bits total)

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These mathematical functions allow integers as well as floating-point numbers as arguments.

- Function:
**sin***arg* - Function:
**cos***arg* - Function:
**tan***arg* These are the basic trigonometric functions, with argument

`arg`measured in radians.

- Function:
**asin***arg* The value of

`(asin`

is a number between -pi/2 and pi/2 (inclusive) whose sine is`arg`)`arg`. If`arg`is out of range (outside [-1, 1]),`asin`

returns a NaN.

- Function:
**acos***arg* The value of

`(acos`

is a number between 0 and pi (inclusive) whose cosine is`arg`)`arg`. If`arg`is out of range (outside [-1, 1]),`acos`

returns a NaN.

- Function:
**atan***y &optional x* The value of

`(atan`

is a number between -pi/2 and pi/2 (exclusive) whose tangent is`y`)`y`. If the optional second argument`x`is given, the value of`(atan y x)`

is the angle in radians between the vector`[`

and the`x`,`y`]`X`

axis.

- Function:
**exp***arg* This is the exponential function; it returns

*e*to the power`arg`.

- Function:
**log***arg &optional base* This function returns the logarithm of

`arg`, with base`base`. If you don’t specify`base`, the natural base*e*is used. If`arg`or`base`is negative,`log`

returns a NaN.

- Function:
**expt***x y* This function returns

`x`raised to power`y`. If both arguments are integers and`y`is positive, the result is an integer; in this case, overflow causes truncation, so watch out. If`x`is a finite negative number and`y`is a finite non-integer,`expt`

returns a NaN.

- Function:
**sqrt***arg* This returns the square root of

`arg`. If`arg`is finite and less than zero,`sqrt`

returns a NaN.

In addition, Emacs defines the following common mathematical constants:

- Variable:
**float-e** The mathematical constant

*e*(2.71828…).

- Variable:
**float-pi** The mathematical constant

*pi*(3.14159…).

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A deterministic computer program cannot generate true random
numbers. For most purposes, *pseudo-random numbers* suffice. A
series of pseudo-random numbers is generated in a deterministic
fashion. The numbers are not truly random, but they have certain
properties that mimic a random series. For example, all possible
values occur equally often in a pseudo-random series.

Pseudo-random numbers are generated from a *seed value*. Starting from
any given seed, the `random`

function always generates the same
sequence of numbers. By default, Emacs initializes the random seed at
startup, in such a way that the sequence of values of `random`

(with overwhelming likelihood) differs in each Emacs run.

Sometimes you want the random number sequence to be repeatable. For
example, when debugging a program whose behavior depends on the random
number sequence, it is helpful to get the same behavior in each
program run. To make the sequence repeat, execute `(random "")`

.
This sets the seed to a constant value for your particular Emacs
executable (though it may differ for other Emacs builds). You can use
other strings to choose various seed values.

- Function:
**random***&optional limit* This function returns a pseudo-random integer. Repeated calls return a series of pseudo-random integers.

If

`limit`is a positive integer, the value is chosen to be nonnegative and less than`limit`. Otherwise, the value might be any integer representable in Lisp, i.e., an integer between`most-negative-fixnum`

and`most-positive-fixnum`

(see section Integer Basics).If

`limit`is`t`

, it means to choose a new seed as if Emacs were restarting, typically from the system entropy. On systems lacking entropy pools, choose the seed from less-random volatile data such as the current time.If

`limit`is a string, it means to choose a new seed based on the string’s contents.

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