stdfix-exp.c File Reference

An implementation of exponential for fixpoint accum. More...

#include "stdfix-exp.h"
#include "utils.h"

Functions
static uint32_t	coef_mult (uint32_t c, uint32_t x)
	Multiplies a coefficient and the variable term correctly and efficiently, implementing multiplication of accum values.
static uint32_t	exp_series (uint32_t x)
	Exponential series, part of implementation of expk()
uint64_t	__expi64 (int_k_t n)
accum	expk (accum x)
	Fixed point exponential.
unsigned accum	expuk (accum x)
	Fixed point exponential.
unsigned long fract	expulr (accum x)
	Fixed point exponential.

Variables
static uint64_t	__exp_hi [26]
	Series to support exponential: upper coefficients.
static uint32_t	__expm1_mid [16]
	Series to support exponential: middle coefficients.
static uint32_t	__exp_series [3] = { 5294, 4293434720, 2081624032 }
	Series to support exponential: lower coefficients.

Detailed Description

An implementation of exponential for fixpoint accum.

Author

Dave Lester (david.nosp@m..r.l.nosp@m.ester.nosp@m.@man.nosp@m.chest.nosp@m.er.a.nosp@m.c.uk)

Copyright

© Dave Lester and The University of Manchester, 2013. All rights reserved. SpiNNaker Project Advanced Processor Technologies Group School of Computer Science The University of Manchester Manchester M13 9PL, UK

Date

20 February, 2014

Function Documentation

coef_mult()

static uint32_t coef_mult ( uint32_t  c, uint32_t  x  )

inlinestatic

Multiplies a coefficient and the variable term correctly and efficiently, implementing multiplication of accum values.

Parameters

[in]	c	a bit-cast accum
[in]	x	a bit-cast accum

Returns

The product, c × x, a bit-cast accum

exp_series()

static uint32_t exp_series ( uint32_t  x )

inlinestatic

Exponential series, part of implementation of expk()

Parameters

[in]

x

The argument

Returns

the result

expk()

accum expk

(

s1615

x

)

Fixed point exponential.

Parameters

[in]

x

Value to compute the exponential of.

Returns

The best approximation to e^x possible in an s1615

expuk()

unsigned accum expuk

(

s1615

x

)

Fixed point exponential.

Parameters

[in]

x

Value to compute the exponential of.

Returns

The best approximation to e^x possible in a u1616

expulr()

unsigned long fract expulr

(

s1615

x

)

Fixed point exponential.

Parameters

[in]

x

Value to compute the exponential of.

Returns

The best approximation to e^x possible in a u032

Variable Documentation

__exp_hi

uint64_t __exp_hi[26]

static

Initial value:

= {
   9708,  26389,          71733,         194991,          530041,         1440801,
        3916503,       10646160,       28939262,        78665070,       213833830,
      581260615,     1580030169,     4294967296,     11674931555,     31735754293,
    86266724208,   234497268814,   637429664642,   1732713474316,   4710003551159,
 12803117065094, 34802480465680, 94602950235157, 257157480542844, 699026506411923
}

Series to support exponential: upper coefficients.

__expm1_mid

uint32_t __expm1_mid[16]

static

Initial value:

= {
        0,  260218914,  504671961,  734314346,
    950043403, 1152702096, 1343082321, 1521927990,
   1689937949, 1847768698, 1996036966, 2135322113,
   2266168400, 2389087112, 2504558555, 2613033936
}

Series to support exponential: middle coefficients.