From 1ae98055d0c5226ce535318b81f32b95da8b7448 Mon Sep 17 00:00:00 2001
From: jjy <jjyruby@gmail.com>
Date: Fri, 17 Jan 2020 17:05:58 +0800
Subject: [PATCH] refactor: remove failure and f64 for no_std

---
 Cargo.toml    |  1 -
 src/error.rs  | 24 +++++++++++++++++++-----
 src/helper.rs | 11 ++++++++++-
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 949c382..34dbfbc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,7 +12,6 @@ default = ["std"]
 std = []
 
 [dependencies]
-failure = "0.1.5"
 cfg-if = "0.1"
 
 [dev-dependencies]
diff --git a/src/error.rs b/src/error.rs
index 108830c..4e246b8 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,12 +1,26 @@
-pub use failure::Fail;
 pub type Result<T> = core::result::Result<T, Error>;
 
-#[derive(Fail, Debug, PartialEq, Eq, Clone)]
+#[derive(Debug, PartialEq, Eq, Clone)]
 pub enum Error {
-    #[fail(display = "Get root on an empty MMR")]
     GetRootOnEmpty,
-    #[fail(display = "Inconsistent store")]
     InconsistentStore,
-    #[fail(display = "Store error {}", _0)]
     StoreError(crate::string::String),
 }
+
+impl core::fmt::Display for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
+        use Error::*;
+        match self {
+            GetRootOnEmpty => write!(f, "Get root on an empty MMR")?,
+            InconsistentStore => write!(f, "Inconsistent store")?,
+            StoreError(msg) => write!(f, "Store error {}", msg)?,
+        }
+        Ok(())
+    }
+}
+
+cfg_if::cfg_if! {
+    if #[cfg(feature = "std")] {
+        impl ::std::error::Error for Error {}
+    }
+}
diff --git a/src/helper.rs b/src/helper.rs
index fe623cb..f90d17b 100644
--- a/src/helper.rs
+++ b/src/helper.rs
@@ -1,5 +1,14 @@
 use crate::vec::Vec;
 
+fn log2(mut n: u64) -> u64 {
+    let mut k = 0;
+    while n > 1 {
+        k += 1;
+        n >>= 1;
+    }
+    k
+}
+
 pub fn leaf_index_to_pos(index: u64) -> u64 {
     if index == 0 {
         return 0;
@@ -10,7 +19,7 @@ pub fn leaf_index_to_pos(index: u64) -> u64 {
     let mut height = 0u32;
     while leaves > 1 {
         // get heighest peak height
-        height = (leaves as f64).log2() as u32;
+        height = log2(leaves) as u32;
         // calculate leaves in peak
         let peak_leaves = 1 << height;
         // heighest positon