OOps... the tabs were garbled
thus again the numbers
...
...
Let's have a look at some numbers!
What follows is the output of a small test program,
computing some common decibel factors. For one, we compute...
10^-exponent vs powf(10, -exponent)
1/10^exponent vs powf(0.1, exponent)
And additionally exp10f(-exponent)
And this with -O0, -03 and then computing with doubles -O0 and -O3
CompileFlags:
-std=gnu++11 -march=athlon64 -m64 -msse -msse2 -mfpmath=sse -ffast-math
-fno-finite-math-only -fomit-frame-pointer -g3 -ggdb
Observations:
* the optimised exp()-from-precomputed-log always
yields same values for 10^-exponent vs 1/10^exponent
* the powf() differs with -O3
* using doubles in our optimised variant yields same values as exp10f
OOps... the tabs were garbled
thus again the numbers
...
...
Let's have a look at some numbers!
What follows is the output of a small test program,
computing some common decibel factors. For one, we compute...
10^-exponent vs powf(10, -exponent)
1/10^exponent vs powf(0.1, exponent)
And additionally exp10f(-exponent)
And this with -O0, -03 and then computing with doubles -O0 and -O3
CompileFlags:> -std=gnu++11 -march=athlon64 -m64 -msse -msse2 -mfpmath=sse
-ffast-math
> -fno-finite-math-only -fomit-frame-pointer -g3 -ggdb
Observations:
* the optimised exp()-from-precomputed-log always
yields same values for 10^-exponent vs 1/10^exponent
* the powf() differs with -O3
* using doubles in our optimised variant yields same values as exp10f
## float with -O0 ##
====== -20dB
1/10^v = 0.099999994 |powf: 0.100000001
10^-v = 0.099999994 |powf: 0.100000001
|exp10f 0.100000001
====== -40dB
1/10^v = 0.00999999978 |powf: 0.0100000007
10^-v = 0.00999999978 |powf: 0.00999999978
|exp10f 0.00999999978
====== -60dB
1/10^v = 0.000999999931 |powf: 0.00100000005
10^-v = 0.000999999931 |powf: 0.00100000005
|exp10f 0.00100000005
====== -100dB
1/10^v = 9.99999338e-06 |powf: 1.00000007e-05
10^-v = 9.99999338e-06 |powf: 9.99999975e-06
|exp10f 9.99999975e-06
## float with -O3 ##
====== -20dB
1/10^v = 0.099999994 |powf: 0.099999994
10^-v = 0.099999994 |powf: 0.099999994
|exp10f 0.100000001
====== -40dB
1/10^v = 0.00999999978 |powf: 0.00999999978
10^-v = 0.00999999978 |powf: 0.00999999978
|exp10f 0.00999999978
====== -60dB
1/10^v = 0.000999999931 |powf: 0.000999999931
10^-v = 0.000999999931 |powf: 0.000999999931
|exp10f 0.00100000005
====== -100dB
1/10^v = 9.99999338e-06 |powf: 9.99999338e-06
10^-v = 9.99999338e-06 |powf: 9.99999338e-06
|exp10f 9.99999975e-06
## double with -O0 ##
====== -20dB
1/10^v = 0.100000001 |powf: 0.100000001
10^-v = 0.100000001 |powf: 0.100000001
|exp10f 0.100000001
====== -40dB
1/10^v = 0.00999999978 |powf: 0.0100000007
10^-v = 0.00999999978 |powf: 0.00999999978
|exp10f 0.00999999978
====== -60dB
1/10^v = 0.00100000005 |powf: 0.00100000005
10^-v = 0.00100000005 |powf: 0.00100000005
|exp10f 0.00100000005
====== -100dB
1/10^v = 9.99999975e-06 |powf: 1.00000007e-05
10^-v = 9.99999975e-06 |powf: 9.99999975e-06
|exp10f 9.99999975e-06
## double with -O3 ##
====== -20dB
1/10^v = 0.100000001 |powf: 0.099999994
10^-v = 0.100000001 |powf: 0.099999994
|exp10f 0.100000001
====== -40dB
1/10^v = 0.00999999978 |powf: 0.00999999978
10^-v = 0.00999999978 |powf: 0.00999999978
|exp10f 0.00999999978
====== -60dB
1/10^v = 0.00100000005 |powf: 0.000999999931
10^-v = 0.00100000005 |powf: 0.000999999931
|exp10f 0.00100000005
====== -100dB
1/10^v = 9.99999975e-06 |powf: 9.99999338e-06
10^-v = 9.99999975e-06 |powf: 9.99999338e-06
|exp10f 9.99999975e-06
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