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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
163 lines
3.7 KiB
Groff
163 lines
3.7 KiB
Groff
.\"
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.\" Copyright (c) 2018 Netflix, Inc.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions, and the following disclaimer,
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.\" without modification, immediately at the beginning of the file.
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.\" 2. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
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.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd July 8, 2018
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.Dt Q_IFRAWMASK 3
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.Os
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.Sh NAME
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.Nm Q_IFRAWMASK ,
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.Nm Q_IFVALIMASK ,
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.Nm Q_IFVALFMASK ,
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.Nm Q_GIFRAW ,
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.Nm Q_GIFABSVAL ,
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.Nm Q_GIFVAL ,
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.Nm Q_SIFVAL ,
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.Nm Q_SIFVALS
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.Nd fixed-point math functions which manipulate the combined integer/fractional
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data bits
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.Sh SYNOPSIS
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.In sys/qmath.h
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.Ft ITYPE
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.Fn Q_IFRAWMASK "QTYPE q"
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.Ft ITYPE
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.Fn Q_IFVALIMASK "QTYPE q"
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.Ft ITYPE
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.Fn Q_IFVALFMASK "QTYPE q"
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.Ft ITYPE
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.Fn Q_GIFRAW "QTYPE q"
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.Ft ITYPE
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.Fn Q_GIFABSVAL "QTYPE q"
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.Ft ITYPE
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.Fn Q_GIFVAL "QTYPE q"
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.Ft QTYPE
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.Fn Q_SIFVAL "QTYPE q" "ITYPE ifv"
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.Ft QTYPE
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.Fn Q_SIFVALS "QTYPE q" "ITYPE iv" "ITYPE fv"
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.Sh DESCRIPTION
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.Fn Q_IFRAWMASK
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returns a
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.Fa q Ns -specific
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bit mask for
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.Fa q Ap s
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combined integer and fractional data bits.
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.Pp
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.Fn Q_IFVALIMASK
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and
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.Fn Q_IFVALFMASK
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return
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.Fa q Ns -specific
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bit masks for the integer and fractional bits of
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.Fa q Ap s
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combined integer and fractional data bits value, i.e., are applicable to the
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values returned by
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.Fn Q_GIFABSVAL
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and
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.Fn Q_GIFVAL .
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.Pp
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.Fn Q_GIFRAW
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returns
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.Fa q Ap s
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raw masked integer/fractional data bits.
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.Pp
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.Fn Q_GIFABSVAL
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and
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.Fn Q_GIFVAL
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return the absolute and real values of
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.Fa q Ap s
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integer/fractional data bits respectively.
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.Pp
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.Fn Q_SIFVAL
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sets
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.Fa q Ap s
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combined integer/fractional data bits to the value
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.Fa ifv ,
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whereas
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.Fn Q_SIFVALS
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independently sets
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.Fa q Ap s
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integer and fractional data bits to the separate values
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.Fa iv
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and
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.Fa fv .
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.Pp
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All of those functions operate on
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the following data types:
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.Vt s8q_t ,
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.Vt u8q_t ,
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.Vt s16q_t ,
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.Vt u16q_t ,
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.Vt s32q_t ,
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.Vt u32q_t ,
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.Vt s64q_t ,
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and
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.Vt u64q_t ,
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which are referred to generically as
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.Fa QTYPE .
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The
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.Fa ITYPE
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refers to the
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.Xr stdint 7
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integer types.
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.Pp
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For more details, see
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.Xr qmath 3 .
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.Sh RETURN VALUES
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.Fn Q_IFRAWMASK ,
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.Fn Q_IFVALIMASK ,
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.Fn Q_IFVALFMASK ,
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.Fn Q_GIFABSVAL ,
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.Fn Q_GIFVAL ,
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.Fn Q_GIFRAW ,
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.Fn Q_GIFABSVAL
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and
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.Fn Q_GIFVAL
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return their respective values as integers of the same underlying ITYPE as
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.Fa q .
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.Pp
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.Fn Q_SIFVAL
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and
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.Fn Q_SIFVALS
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return the value of
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.Fa q
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post change.
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.Sh SEE ALSO
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.Xr errno 2 ,
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.Xr qmath 3 ,
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.Xr stdint 7
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.Sh HISTORY
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The
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.Xr qmath 3
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functions first appeared in
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.Fx 13.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Xr qmath 3
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functions and this manual page were written by
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.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org
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and sponsored by Netflix, Inc.
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