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Merge pull request #271 from michaelsproul/log-int

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Fix log_int implementation, removing floats
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Age Manning 2019-03-03 00:13:55 +11:00 committed by GitHub
commit 684ef9f74c
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2 changed files with 15 additions and 15 deletions
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1
eth2/fork_choice/Cargo.toml
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@ -8,7 +8,6 @@ edition = "2018"
db = { path = "../../beacon_node/db" } db = { path = "../../beacon_node/db" }
ssz = { path = "../utils/ssz" } ssz = { path = "../utils/ssz" }
types = { path = "../types" } types = { path = "../types" }
fast-math = "0.1.1"
log = "0.4.6" log = "0.4.6"
bit-vec = "0.5.0" bit-vec = "0.5.0"

29
eth2/fork_choice/src/bitwise_lmd_ghost.rs
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@ -1,5 +1,5 @@
//! The optimised bitwise LMD-GHOST fork choice rule.
extern crate bit_vec; extern crate bit_vec;
extern crate fast_math;
use crate::{ForkChoice, ForkChoiceError}; use crate::{ForkChoice, ForkChoiceError};
use bit_vec::BitVec; use bit_vec::BitVec;
@ -7,7 +7,6 @@ use db::{
stores::{BeaconBlockStore, BeaconStateStore}, stores::{BeaconBlockStore, BeaconStateStore},
ClientDB, ClientDB,
}; };
use fast_math::log2_raw;
use log::{debug, trace}; use log::{debug, trace};
use std::collections::HashMap; use std::collections::HashMap;
use std::sync::Arc; use std::sync::Arc;
@ -19,22 +18,17 @@ use types::{
//TODO: Pruning - Children //TODO: Pruning - Children
//TODO: Handle Syncing //TODO: Handle Syncing
/// The optimised bitwise LMD-GHOST fork choice rule. // NOTE: This uses u32 to represent difference between block heights. Thus this is only
/// NOTE: This uses u32 to represent difference between block heights. Thus this is only // applicable for block height differences in the range of a u32.
/// applicable for block height differences in the range of a u32. // This can potentially be parallelized in some parts.
/// This can potentially be parallelized in some parts.
// we use fast log2, a log2 lookup table is implemented in Vitaliks code, potentially do /// Compute the base-2 logarithm of an integer, floored (rounded down)
// the comparison. Log2_raw takes 2ns according to the documentation.
#[inline] #[inline]
fn log2_int(x: u32) -> u32 { fn log2_int(x: u32) -> u32 {
if x == 0 { if x == 0 {
return 0; return 0;
} }
assert!( 31 - x.leading_zeros()
x <= std::f32::MAX as u32,
"Height too large for fast log in bitwise fork choice"
);
log2_raw(x as f32) as u32
} }
fn power_of_2_below(x: u32) -> u32 { fn power_of_2_below(x: u32) -> u32 {
@ -469,7 +463,6 @@ mod tests {
#[test] #[test]
pub fn test_power_of_2_below() { pub fn test_power_of_2_below() {
println!("{:?}", std::f32::MAX);
assert_eq!(power_of_2_below(4), 4); assert_eq!(power_of_2_below(4), 4);
assert_eq!(power_of_2_below(5), 4); assert_eq!(power_of_2_below(5), 4);
assert_eq!(power_of_2_below(7), 4); assert_eq!(power_of_2_below(7), 4);
@ -478,4 +471,12 @@ mod tests {
assert_eq!(power_of_2_below(33), 32); assert_eq!(power_of_2_below(33), 32);
assert_eq!(power_of_2_below(63), 32); assert_eq!(power_of_2_below(63), 32);
} }
#[test]
pub fn test_power_of_2_below_large() {
let pow: u32 = 1 << 24;
for x in (pow - 20)..(pow + 20) {
assert!(power_of_2_below(x) <= x, "{}", x);
}
}
} }