2 .\" Copyright (c) 2018 Netflix, Inc.
3 .\" All rights reserved.
5 .\" Redistribution and use in source and binary forms, with or without
6 .\" modification, are permitted provided that the following conditions
8 .\" 1. Redistributions of source code must retain the above copyright
9 .\" notice, this list of conditions, and the following disclaimer,
10 .\" without modification, immediately at the beginning of the file.
11 .\" 2. The name of the author may not be used to endorse or promote products
12 .\" derived from this software without specific prior written permission.
14 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
18 .\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 .Nd fixed-point math library based on the
41 data types and APIs support fixed-point math based on the
44 The APIs have been built around the following data types:
54 which are referred to generically in the earlier API definitions as
62 is used to refer to any numeric type and is therefore a superset of
67 This scheme can represent Q numbers with
68 .Bq 2, 4, 6, 8, 16, 32, 48
69 bits of precision after the binary radix point,
74 The number of bits available for the integral component is not explicitly
75 specified, and implicitly consumes the remaining available bits of the chosen Q
78 Operations on Q numbers maintain the precision of their arguments.
79 The fractional component is truncated to fit into the destination,
81 None of the operations is affected by the floating-point environment.
83 For more details, see the
84 .Sx IMPLEMENTATION DETAILS
88 .Bl -column "isgreaterequal" "bessel function of the second kind of the order 0"
89 .Em "Name Description"
91 .Ss Functions which create/initialise a Q number
93 .Xr Q_INI 3 initialise a Q number
95 .Ss Numeric functions which operate on two Q numbers
97 .Xr Q_QADDQ 3 addition
98 .Xr Q_QDIVQ 3 division
99 .Xr Q_QMULQ 3 multiplication
100 .Xr Q_QSUBQ 3 subtraction
101 .Xr Q_NORMPREC 3 normalisation
102 .Xr Q_QMAXQ 3 maximum function
103 .Xr Q_QMINQ 3 minimum function
104 .Xr Q_QCLONEQ 3 identical copy
105 .Xr Q_QCPYVALQ 3 representational copy
107 .Ss Numeric functions which apply integers to a Q number
109 .Xr Q_QADDI 3 addition
110 .Xr Q_QDIVI 3 division
111 .Xr Q_QMULI 3 multiplication
112 .Xr Q_QSUBI 3 subtraction
113 .Xr Q_QFRACI 3 fraction
114 .Xr Q_QCPYVALI 3 overwrite
116 .Ss Numeric functions which operate on a single Q number
118 .Xr Q_QABS 3 absolute value
119 .Xr Q_Q2D 3 double representation
120 .Xr Q_Q2F 3 float representation
122 .Ss Comparison and logic functions
124 .Xr Q_SIGNED 3 determine sign
125 .Xr Q_LTZ 3 less than zero
126 .Xr Q_PRECEQ 3 compare bits
127 .Xr Q_QLTQ 3 less than
128 .Xr Q_QLEQ 3 less or equal
129 .Xr Q_QGTQ 3 greater than
130 .Xr Q_QGEQ 3 greater or equal
132 .Xr Q_QNEQ 3 not equal
133 .Xr Q_OFLOW 3 would overflow
134 .Xr Q_RELPREC 3 relative precision
136 .Ss Functions which manipulate the control/sign data bits
138 .Xr Q_SIGNSHFT 3 sign bit position
139 .Xr Q_SSIGN 3 sign bit
140 .Xr Q_CRAWMASK 3 control bitmask
141 .Xr Q_SRAWMASK 3 sign bitmask
142 .Xr Q_GCRAW 3 raw control bits
143 .Xr Q_GCVAL 3 value of control bits
144 .Xr Q_SCVAL 3 set control bits
146 .Ss Functions which manipulate the combined integer/fractional data bits
148 .Xr Q_IFRAWMASK 3 integer/fractional bitmask
149 .Xr Q_IFVALIMASK 3 value of integer bits
150 .Xr Q_IFVALFMASK 3 value of fractional bits
151 .Xr Q_GIFRAW 3 raw integer/fractional bits
152 .Xr Q_GIFABSVAL 3 absolute value of fractional bits
153 .Xr Q_GIFVAL 3 real value of fractional bits
154 .Xr Q_SIFVAL 3 set integer/fractional bits
155 .Xr Q_SIFVALS 3 set separate integer/fractional values
157 .Ss Functions which manipulate the integer data bits
159 .Xr Q_IRAWMASK 3 integer bitmask
160 .Xr Q_GIRAW 3 raw integer bits
161 .Xr Q_GIABSVAL 3 absolute value of integer bits
162 .Xr Q_GIVAL 3 real value of integer bits
163 .Xr Q_SIVAL 3 set integer bits
165 .Ss Functions which manipulate the fractional data bits
167 .Xr Q_FRAWMASK 3 fractional bitmask
168 .Xr Q_GFRAW 3 raw fractional bits
169 .Xr Q_GFABSVAL 3 absolute value of fractional bits
170 .Xr Q_GFVAL 3 real value of fractional bits
171 .Xr Q_SFVAL 3 set fractional bits
173 .Ss Miscellaneous functions/variables
175 .Xr Q_NCBITS 3 number of reserved control bits
176 .Xr Q_BT 3 C data type
177 .Xr Q_TC 3 casted data type
178 .Xr Q_NTBITS 3 number of total bits
179 .Xr Q_NFCBITS 3 number of control-encoded fractional bits
180 .Xr Q_MAXNFBITS 3 number of maximum fractional bits
181 .Xr Q_NFBITS 3 number of effective fractional bits
182 .Xr Q_NIBITS 3 number of integer bits
183 .Xr Q_RPSHFT 3 bit position of radix point
184 .Xr Q_ABS 3 absolute value
185 .Xr Q_MAXSTRLEN 3 number of characters to render string
186 .Xr Q_TOSTR 3 render string
187 .Xr Q_SHL 3 left-shifted value
188 .Xr Q_SHR 3 right-shifted value
189 .Xr Q_DEBUG 3 render debugging information
190 .Xr Q_DFV2BFV 3 convert decimal fractional value
192 .Sh IMPLEMENTATION DETAILS
195 data types and APIs support fixed-point math based on the
198 This implementation uses the Q notation
202 specifies the number of bits for integral data
203 .Pq excluding the sign bit for signed types ,
206 specifies the number of bits for fractional data.
208 The APIs have been built around the following q_t derived data types:
209 .Bd -literal -offset indent
210 typedef int8_t s8q_t;
211 typedef uint8_t u8q_t;
212 typedef int16_t s16q_t;
213 typedef uint16_t u16q_t;
214 typedef int32_t s32q_t;
215 typedef uint32_t u32q_t;
216 typedef int64_t s64q_t;
217 typedef uint64_t u64q_t;
220 These types are referred to generically in the earlier API definitions as
226 integer types the Q data types are derived from.
228 is used to refer to any numeric type and is therefore a superset of
233 The 3 least significant bits
235 of all q_t data types are reserved for embedded control data:
238 bits 1-2 specify the binary radix point shift index operand, with 00,01,10,11 ==
241 bit 3 specifies the radix point shift index operand multiplier as 2
247 This scheme can therefore represent Q numbers with
248 .Bq 2,4,6,8,16,32,48,64
249 bits of precision after the binary radix point.
250 The number of bits available for the integral component is not explicitly
251 specified, and implicitly consumes the remaining available bits of the chosen Q
254 Additionally, the most significant bit
256 of signed Q types stores the sign bit, with bit value 0 representing a positive
257 number and bit value 1 representing a negative number.
258 Negative numbers are stored as absolute values with the sign bit set, rather
259 than the more typical two's complement representation.
260 This avoids having to bit shift negative numbers, which can result in undefined
261 behaviour from some compilers.
263 This binary representation used for Q numbers therefore comprises a set of
264 distinct data bit types and associated bit counts.
265 Data bit types/labels, listed in LSB to MSB order, are: control
273 The following example illustrates the binary representation of a Q20.8 number
274 represented using a s32q_t variable:
275 .Bd -literal -offset indent
280 3 3 2 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1
281 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
283 S I I I I I I I I I I I I I I I I I I I I F F F F F F F F C C C
286 Important bit counts are: total, control, control-encoded fractional, maximum
287 fractional, effective fractional and integer bits.
289 The count of total bits is derived from the size of the q_t data type.
290 For example, a s32q_t has 32 total bits.
292 The count of control-encoded fractional bits is derived from calculating the
293 number of fractional bits per the control bit encoding scheme.
294 For example, the control bits binary value of 101 encodes a fractional bit
295 count of 2 x 16 = 32 fractional bits.
297 The count of maximum fractional bits is derived from the difference between the
298 counts of total bits and control/sign bits.
299 For example, a s32q_t has a maximum of 32 - 3 - 1 = 28 fractional bits.
301 The count of effective fractional bits is derived from the minimum of the
302 control-encoded fractional bits and the maximum fractional bits.
303 For example, a s32q_t with 32 control-encoded fractional bits is effectively
304 limited to 28 fractional bits.
306 The count of integer bits is derived from the difference between the counts of
307 total bits and all other non-integer data bits
308 .Pq the sum of control, fractional and sign bits.
309 For example, a s32q_t with 8 effective fractional bits has 32 - 3 - 8 - 1 = 20 integer
311 The count of integer bits can be zero if all available numeric data bits have
312 been reserved for fractional data, e.g., when the number of control-encoded
313 fractional bits is greater than or equal to the underlying Q data type's maximum
316 .Ss Calculating area of a circle with r=4.2 and rpshft=16
317 .Bd -literal -offset indent
322 Q_INI(&pi, 3, 14159, 16);
329 Q_TOSTR(a, -1, 10, buf, sizeof(buf));
330 printf("%s\\n", buf);
333 Declare a Q20.8 s32q_t number
335 initialise it with the fixed-point value for 5/3, and render a debugging
336 representation of the variable
337 .Pq including its full precision decimal C-string representation ,
339 .Bd -literal -offset indent
341 Q_INI(&s32, 0, 0, 8);
342 Q_QFRACI(&s32, 5, 3);
343 char buf[Q_MAXSTRLEN(s32, 10)];
344 Q_TOSTR(s32, -1, 10, buf, sizeof(buf));
345 printf(Q_DEBUG(s32, "", "\\n\\ttostr=%s\\n\\n", 0), buf);
348 The above code outputs the following to the console:
349 .Bd -literal -offset indent
351 type=s32q_t, Qm.n=Q20.8, rpshft=11, imin=0xfff00001, \\
354 imask=0x7ffff800, fmask=0x000007f8, cmask=0x00000007, \\
356 iraw=0x00000800, iabsval=0x1, ival=0x1
357 fraw=0x00000550, fabsval=0xaa, fval=0xaa
363 present in the rendered output above indicates a manual line break inserted to
364 keep the man page within 80 columns and is not part of the actual output.
381 functions first appeared in
387 functions and this manual page were written by
388 .An Lawrence Stewart Aq Mt lstewart@FreeBSD.org
389 and sponsored by Netflix, Inc.