▼ |  | Reference: PLT Scheme

1 | Language Model
2 | Syntactic Forms
3 | Datatypes
4 | Structures
5 | Classes and Objects
6 | Units
7 | Contracts
8 | Pattern Matching
9 | Control Flow
10 | Concurrency
11 | Macros
12 | Input and Output
13 | Reflection and Security
14 | Operating System
15 | Memory Management
16 | Unsafe Operations
17 | Running PLT Scheme
| Bibliography
| Index

► | 16 | Unsafe Operations

16.1 | Unsafe Numeric Operations
16.2 | Unsafe Data Extraction

On this page:

16.1`` Unsafe Numeric Operations
unsafe-fx+
unsafe-fx-
unsafe-fx*
unsafe-fxquotient
unsafe-fxremainder
unsafe-fxmodulo
unsafe-fxabs
unsafe-fxand
unsafe-fxior
unsafe-fxxor
unsafe-fxnot
unsafe-fxlshift
unsafe-fxrshift
unsafe-fx=
unsafe-fx<
unsafe-fx>
unsafe-fx<=
unsafe-fx>=
unsafe-fxmin
unsafe-fxmax
unsafe-fx->fl
unsafe-fl+
unsafe-fl-
unsafe-fl*
unsafe-fl/
unsafe-flabs
unsafe-fl=
unsafe-fl<
unsafe-fl>
unsafe-fl<=
unsafe-fl>=
unsafe-flmin
unsafe-flmax
unsafe-flround
unsafe-flfloor
unsafe-flceiling
unsafe-fltruncate
unsafe-flsin
unsafe-flcos
unsafe-fltan
unsafe-flasin
unsafe-flacos
unsafe-flatan
unsafe-fllog
unsafe-flexp
unsafe-flsqrt
16.2`` Unsafe Data Extraction
unsafe-car
unsafe-cdr
unsafe-mcar
unsafe-mcdr
unsafe-set-mcar!
unsafe-set-mcdr!
unsafe-vector-length
unsafe-vector-ref
unsafe-vector-set!
unsafe-string-length
unsafe-string-ref
unsafe-string-set!
unsafe-bytes-length
unsafe-bytes-ref
unsafe-bytes-set!
unsafe-flvector-length
unsafe-flvector-ref
unsafe-flvector-set!
unsafe-f64vector-ref
unsafe-f64vector-set!
unsafe-struct-ref
unsafe-struct-set!

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### 16`` Unsafe Operations

(require scheme/unsafe/ops)

All fuctions and forms provided by scheme/base and scheme check their arguments to ensure that the arguments conform to contracts and other constraints. For example, vector-ref checks its arguments to ensure that the first argument is a vector, that the second argument is an exact integer, and that the second argument is between 0 and one less than the vector’s length, inclusive.

Functions provided by scheme/unsafe/ops are unsafe. They have certain constraints, but the constraints are not checked, which allows the system to generate and execute faster code. If arguments violate an unsafe function’s constraints, the function’s behavior and result is unpredictable, and the entire system can crash or become corrupted.

All of the exported bindings of scheme are protected in the sense of protect-out, so access to unsafe operations can be prevented by adjusting the code inspector (see Code Inspectors).

#### 16.1`` Unsafe Numeric Operations

(unsafe-fx+ a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fx- a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fx* a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxquotient a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxremainder a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxmodulo a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxabs a) → fixnum?
a : fixnum?

For fixnums: Like +, -, *, quotient, remainder, modulo, and abs, but constrained to consume fixnums and produce a fixnum result. The mathematical operation on a and b must be representable as a fixnum. In the case of unsafe-fxquotient, unsafe-fxremainder, and unsafe-fxmodulo, b must not be 0.

(unsafe-fxand a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxior a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxxor a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxnot a) → fixnum?
a : fixnum?

(unsafe-fxlshift a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxrshift a b) → fixnum?
a : fixnum?
b : fixnum?

For fixnums: Like bitwise-and, bitwise-ior, bitwise-xor, bitwise-not, and arithmetic-shift, but constrained to consume fixnums; the result is always a fixnum. The unsafe-fxlshift and unsafe-fxrshift operations correspond to arithmetic-shift, but require non-negative arguments; unsafe-fxlshift is a positive (i.e., left) shift, and unsafe-fxrshift is a negative (i.e., right) shift, where the number of bits to shift must be less than the number of bits used to represent a fixnum, and the result is effectively bitwise-anded with the most negative fixnum.

(unsafe-fx= a b) → boolean?
a : fixnum?
b : fixnum?

(unsafe-fx< a b) → boolean?
a : fixnum?
b : fixnum?

(unsafe-fx> a b) → boolean?
a : fixnum?
b : fixnum?

(unsafe-fx<= a b) → boolean?
a : fixnum?
b : fixnum?

(unsafe-fx>= a b) → boolean?
a : fixnum?
b : fixnum?

(unsafe-fxmin a b) → fixnum?
a : fixnum?
b : fixnum?

(unsafe-fxmax a b) → fixnum?
a : fixnum?
b : fixnum?

For fixnums: Like =, <, >, <=, >=, min, and max, but constrained to consume fixnums.

(unsafe-fx->fl a) → inexact-real?
a : fixnum?

Unchecked version of ->fl.

(unsafe-fl+ a b) → inexact-real?
a : inexact-real?
b : inexact-real?

(unsafe-fl- a b) → inexact-real?
a : inexact-real?
b : inexact-real?

(unsafe-fl* a b) → inexact-real?
a : inexact-real?
b : inexact-real?

(unsafe-fl/ a b) → inexact-real?
a : inexact-real?
b : inexact-real?

(unsafe-flabs a) → inexact-real?
a : inexact-real?

For flonums: Unchecked versions of fl+, fl-, fl*, fl/, and flabs.

(unsafe-fl= a b) → boolean?
a : inexact-real?
b : inexact-real?

(unsafe-fl< a b) → boolean?
a : inexact-real?
b : inexact-real?

(unsafe-fl> a b) → boolean?
a : inexact-real?
b : inexact-real?

(unsafe-fl<= a b) → boolean?
a : inexact-real?
b : inexact-real?

(unsafe-fl>= a b) → boolean?
a : inexact-real?
b : inexact-real?

(unsafe-flmin a) → inexact-real?
a : inexact-real?

(unsafe-flmax a) → inexact-real?
a : inexact-real?

For flonums: Unchecked versions of fl=, fl<, fl>, fl<=, fl>=, flmin, and flmax.

(unsafe-flround a) → inexact-real?
a : inexact-real?

(unsafe-flfloor a) → inexact-real?
a : inexact-real?

(unsafe-flceiling a) → inexact-real?
a : inexact-real?

(unsafe-fltruncate a) → inexact-real?
a : inexact-real?

For flonums: Unchecked (potentially) versions of flround, flfloor, flceiling, and fltruncate. Currently, these bindings are simply aliases for the corresponding safe bindings.

(unsafe-flsin a) → inexact-real?
a : inexact-real?

(unsafe-flcos a) → inexact-real?
a : inexact-real?

(unsafe-fltan a) → inexact-real?
a : inexact-real?

(unsafe-flasin a) → inexact-real?
a : inexact-real?

(unsafe-flacos a) → inexact-real?
a : inexact-real?

(unsafe-flatan a) → inexact-real?
a : inexact-real?

(unsafe-fllog a) → inexact-real?
a : inexact-real?

(unsafe-flexp a) → inexact-real?
a : inexact-real?

(unsafe-flsqrt a) → inexact-real?
a : inexact-real?

For flonums: Unchecked (potentially) versions of flsin, flcos, fltan, flasin, flacos, flatan, fllog, flexp, and flsqrt. Currently, some of these bindings are simply aliases for the corresponding safe bindings.

#### 16.2`` Unsafe Data Extraction

(unsafe-car p) → any/c
p : pair?

(unsafe-cdr p) → any/c
p : pair?

(unsafe-mcar p) → any/c
p : mpair?

(unsafe-mcdr p) → any/c
p : mpair?

(unsafe-set-mcar! p v) → void?
p : mpair?
v : any/c

(unsafe-set-mcdr! p v) → void?
p : mpair?
v : any/c

Unsafe variants of car, cdr, mcar, mcdr, set-mcar!, and set-mcdr!.

(unsafe-vector-length v) → fixnum?
v : vector?

(unsafe-vector-ref v k) → any/c
v : vector?
k : fixnum?

(unsafe-vector-set! v k val) → void?
v : vector?
k : fixnum?
val : any/c

Unsafe versions of vector-length, vector-ref, and vector-set!. A vector’s size can never be larger than a fixnum (so even vector-length always returns a fixnum).

(unsafe-string-length str) → fixnum?
str : string?

(unsafe-string-ref str k)
→ (and/c char? (lambda (ch) (<= 0 (char->integer ch) 255)))
str : string?
k : fixnum?

(unsafe-string-set! str k ch) → void?
str : (and/c string? (not/c immutable?))
k : fixnum?
ch : char?

Unsafe versions of string-length, string-ref, and string-set!. The unsafe-string-ref procedure can be used only when the result will be a Latin-1 character. A string’s size can never be larger than a fixnum (so even string-length always returns a fixnum).

(unsafe-bytes-length bstr) → fixnum?
bstr : bytes?

(unsafe-bytes-ref bstr k) → byte?
bstr : bytes?
k : fixnum?

(unsafe-bytes-set! bstr k b) → void?
bstr : (and/c bytes? (not/c immutable?))
k : fixnum?
b : byte?

Unsafe versions of bytes-length, bytes-ref, and bytes-set!. A bytes’s size can never be larger than a fixnum (so even bytes-length always returns a fixnum).

(unsafe-flvector-length v) → fixnum?
v : flvector?

(unsafe-flvector-ref v k) → any/c
v : flvector?
k : fixnum?

(unsafe-flvector-set! v k x) → void?
v : flvector?
k : fixnum?
x : inexact-real?

Unsafe versions of flvector-length, flvector-ref, and flvector-set!. A flvector’s size can never be larger than a fixnum (so even flvector-length always returns a fixnum).

(unsafe-f64vector-ref vec k) → inexact-real?
vec : f64vector?
k : fixnum?

(unsafe-f64vector-set! vec k n) → void?
vec : f64vector?
k : fixnum?
n : inexact-real?

Unsafe versions of f64vector-ref and f64vector-set!.

(unsafe-struct-ref v k) → any/c
v : any/c
k : fixnum?

(unsafe-struct-set! v k val) → void?
v : any/c
k : fixnum?
val : any/c

Unsafe field access and update for an instance of a structure type. The index k must be between 0 (inclusive) and the number of fields in the struture (exclusive). In the case of unsafe-struct-set!, the field must be mutable.
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