5a38af1fb8
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
176 lines
4.1 KiB
Groff
176 lines
4.1 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_QADDQ 3
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.Os
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.Sh NAME
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.Nm Q_QADDQ ,
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.Nm Q_QDIVQ ,
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.Nm Q_QMULQ ,
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.Nm Q_QSUBQ ,
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.Nm Q_NORMPREC ,
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.Nm Q_QMAXQ ,
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.Nm Q_QMINQ ,
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.Nm Q_QCLONEQ ,
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.Nm Q_CPYVALQ
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.Nd fixed-point math functions which operate on two Q numbers
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.Sh SYNOPSIS
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.In sys/qmath.h
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.Ft int
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.Fn Q_QADDQ "QTYPE *a" "QTYPE b"
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.Ft int
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.Fn Q_QDIVQ "QTYPE *a" "QTYPE b"
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.Ft int
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.Fn Q_QMULQ "QTYPE *a" "QTYPE b"
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.Ft int
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.Fn Q_QSUBQ "QTYPE *a" "QTYPE b"
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.Ft int
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.Fn Q_NORMPREC "QTYPE *a" "QTYPE *b"
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.Ft QTYPE
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.Fn Q_QMAXQ "QTYPE a" "QTYPE b"
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.Ft QTYPE
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.Fn Q_QMINQ "QTYPE a" "QTYPE b"
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.Ft int
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.Fn Q_QCLONEQ "QTYPE *l" "QTYPE r"
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.Ft int
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.Fn Q_QCPYVALQ "QTYPE *l" "QTYPE r"
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.Sh DESCRIPTION
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The
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.Fn Q_QADDQ ,
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.Fn Q_QDIVQ ,
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.Fn Q_QMULQ ,
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and
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.Fn Q_QSUBQ
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functions add, divide, multiply or subtract
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.Fa b
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to/by/from
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.Fa a
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respectively, storing the result in
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.Fa a .
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Both arguments must be initialized with the same fractional radix point.
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.Pp
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The
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.Fn Q_NORMPREC
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function attempts to normalise the precision of
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.Fa a
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and
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.Fa b
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if they differ.
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The greater of the two precisions is preferred if possible, unless that would
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truncate integer component data for the other operand, in which case the highest
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precision that preserves the integer component of both
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.Fa a
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and
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.Fa b
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is selected.
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.Pp
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The
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.Fn Q_QMAXQ
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and
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.Fn Q_QMINQ
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functions return the larger or smaller of
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.Fa a
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and
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.Fa b
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respectively.
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.Pp
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The
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.Fn Q_QCLONEQ
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and
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.Fn Q_QCPYVALQ
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functions attempt to store identical or representational copies of
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.Fa r ,
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in
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.Fa l
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respectively.
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An identical Q number produced by cloning copies the control bits as well as the
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verbatim integer/fractional bits.
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A representational copy only copies the values of
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.Fa r Ap s
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integer and fractional bits, representing them in the bits available per
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.Fa l Ap s
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Q format.
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.Pp
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All of those functions operate on 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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.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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The
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.Fn Q_QADDQ ,
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.Fn Q_QDIVQ ,
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.Fn Q_QMULQ ,
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.Fn Q_QSUBQ
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.Fn Q_NORMPREC ,
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.Fn Q_QCLONEQ
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and
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.Fn Q_QCPYVALQ
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functions return 0 on success, or an errno on failure.
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.Er EINVAL
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is returned for divide-by-zero.
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.Er EOVERFLOW
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and
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.Er ERANGE
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are returned for overflow and underflow respectively.
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.Er ERANGE is also returned when the precision of arguments
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does not match.
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.Pp
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The
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.Fn Q_QMAXQ
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and
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.Fn Q_QMINQ
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functions return the numerically larger or smaller of their two inputs
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respectively.
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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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