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Logarithm of 2 (Algorithm)
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package main | |
import "fmt" | |
import "math" | |
func log2(f float64) (float64) { | |
frac, exp := math.Frexp(f) | |
exp-- | |
frac*=2 | |
log := float64(0) | |
part := float64(1) | |
for i := 0 ; i<32; i++ { | |
/* frac >= 2.0 */ | |
if frac>1.999999999999 { | |
log += part | |
frac /= 2 | |
} | |
frac *= frac | |
part /= 2 | |
} | |
return float64(exp)+log | |
} | |
func main(){ | |
for i := 0; i<11; i++ { | |
f := float64(i)/10.0 | |
e := math.Exp2(f) | |
fmt.Printf("%f\t%f\t%f\n",f,math.Log2(e),log2(e)) | |
} | |
} |
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package main | |
import "fmt" | |
import "math" | |
import "math/bits" | |
func log2(f float64) (float64) { | |
frac, exp := math.Frexp(f) | |
exp-- | |
frac*=2 | |
log := float64(0) | |
part := float64(1) | |
for i := 0 ; i<32 ; i++ { | |
/* frac >= 2.0 */ | |
if frac>1.999999999999 { | |
log += part | |
frac /= 2 | |
} | |
frac *= frac | |
part /= 2 | |
} | |
return float64(exp)+log | |
} | |
func main2(){ | |
for i := 0; i<11; i++ { | |
f := float64(i)/10.0 | |
e := math.Exp2(f) | |
fmt.Printf("%f\t%f\t%f\n",f,math.Log2(e),log2(e)) | |
} | |
} | |
func lshift(i uint64,s int) uint64 { | |
if s<0 { return i >> uint(-s) } | |
return i << uint(s) | |
} | |
func ilog2(i int) (float64) { | |
const TWO = 1<<31 | |
exp := bits.Len(uint(i)) | |
exp-- | |
frac := lshift(uint64(i),30-exp) | |
log := float64(exp) | |
part := float64(1) | |
for i := 0 ; i<30 ; i++ { | |
if frac>=TWO { | |
frac >>= 1 | |
log += part | |
} else { | |
} | |
part /= 2 | |
frac = (frac*frac)>>30 | |
} | |
return log | |
} | |
func ilog2n(i,n int) (int) { | |
const TWO = 1<<31 | |
exp := bits.Len(uint(i)) | |
exp-- | |
frac := lshift(uint64(i),30-exp) | |
log := exp*n | |
part := n | |
for i := 0 ; i<30 ; i++ { | |
if frac>=TWO { | |
frac >>= 1 | |
log += part | |
} else { | |
} | |
part /= 2 | |
frac = (frac*frac)>>30 | |
} | |
return log | |
} | |
func main(){ | |
for i := 1; i<10; i++ { | |
f := float64(i) | |
//fmt.Printf("%f\t%f\t%f\n",f,math.Log2(f),ilog2(i)) | |
fmt.Printf("%f\t%f\t%d\n",math.Log2(f),ilog2(i),ilog2n(i,100)/33) | |
//fmt.Printf("%f\t%f\t%f\t%f\n",f,math.Log2(f),log2(f),ilog2(i)) | |
} | |
} |
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