freebsd-dev/share/man/man3/Q_IRAWMASK.3
Edward Tomasz Napierala 5a38af1fb8 Introduce <sys/qmath.h>, a fixed-point math library from Netflix.
This makes it possible to perform mathematical operations
on
fractional values without using floating point. It operates on Q
numbers, which are integer-sized, opaque structures initialized
to hold a chosen number of integer and fractional
bits.


For a general description of the Q number system, see the "Fixed Point
Representation & Fractional Math" whitepaper[1]; for the actual
API see the qmath(3) man page.

This is one of dependencies for the upcoming stats(3) framework[2]
that will be applied to the TCP stack in a later commit.

1. https://www.superkits.net/whitepapers/Fixed%20Point%20Representation%20&%20Fractional%20Math.pdf
2. https://reviews.freebsd.org/D20477

Reviewed by:	bcr (man pages, earlier version), sef (earlier version)
Discussed with:	cem, dteske, imp, lstewart
Sponsored By:	Klara Inc, Netflix
Obtained from:	Netflix
Differential Revision:	https://reviews.freebsd.org/D20116
2019-08-27 11:46:22 +00:00

126 lines
2.9 KiB
Groff

.\"
.\" Copyright (c) 2018 Netflix, Inc.
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.\" $FreeBSD$
.\"
.Dd July 8, 2018
.Dt Q_IRAWMASK 3
.Os
.Sh NAME
.Nm Q_IRAWMASK ,
.Nm Q_GIRAW ,
.Nm Q_GIABSVAL ,
.Nm Q_GIVAL ,
.Nm Q_SIVAL
.Nd fixed-point math functions which manipulate the integer data bits
.Sh SYNOPSIS
.In sys/qmath.h
.Ft ITYPE
.Fn Q_IRAWMASK "QTYPE q"
.Ft ITYPE
.Fn Q_GIRAW "QTYPE q"
.Ft ITYPE
.Fn Q_GIABSVAL "QTYPE q"
.Ft ITYPE
.Fn Q_GIVAL "QTYPE q"
.Ft QTYPE
.Fn Q_SIVAL "QTYPE q" "ITYPE iv"
.Sh DESCRIPTION
.Fn Q_IRAWMASK
returns a
.Fa q Ns -specific
bit mask for
.Fa q Ap s
integer data bits.
.Pp
.Fn Q_GIRAW
returns
.Fa q Ap s
raw masked integer data bits.
.Pp
.Fn Q_GIABSVAL
and
.Fn Q_GIVAL
return the absolute and real values of
.Fa q Ap s
integer data bits respectively.
.Pp
.Fn Q_SIVAL
sets
.Fa q Ap s
integer data bits to the value
.Fa iv .
.Pp
All of those functions operate on
the following data types:
.Vt s8q_t ,
.Vt u8q_t ,
.Vt s16q_t ,
.Vt u16q_t ,
.Vt s32q_t ,
.Vt u32q_t ,
.Vt s64q_t ,
and
.Vt u64q_t ,
which are referred to generically as
.Fa QTYPE .
The
.Fa ITYPE
refers to the
.Xr stdint 7
integer types.
.Pp
For more details, see
.Xr qmath 3 .
.Sh RETURN VALUES
.Fn Q_IRAWMASK ,
.Fn Q_GIRAW ,
.Fn Q_GIABSVAL
and
.Fn Q_GIVAL
return their respective values as integers of the same underlying ITYPE as
.Fa q .
.Pp
.Fn Q_SIVAL
returns the value of
.Fa q
post change.
.Sh SEE ALSO
.Xr errno 2 ,
.Xr qmath 3 ,
.Xr stdint 7
.Sh HISTORY
The
.Xr qmath 3
functions first appeared in
.Fx 13.0 .
.Sh AUTHORS
.An -nosplit
The
.Xr qmath 3
functions and this manual page were written by
.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org
and sponsored by Netflix, Inc.