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Remove u128-support feature and arithmetic 

Closes #2.
This commit is contained in:
Jack Grigg 2018-07-02 21:19:20 +01:00
parent 69ce66ae6c
commit 0eb9f5040b
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2 changed files with 0 additions and 81 deletions
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1
Cargo.toml
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@ -15,5 +15,4 @@ ff_derive = { version = "0.3.0", path = "ff_derive", optional = true }
[features]
default = []
u128-support = []
derive = ["ff_derive"]

80
src/lib.rs
View File

@ -349,7 +349,6 @@ fn test_bit_iterator() {
pub use self::arith_impl::*;
#[cfg(feature = "u128-support")]
mod arith_impl {
/// Calculate a - b - borrow, returning the result and modifying
/// the borrow value.
@ -384,82 +383,3 @@ mod arith_impl {
tmp as u64
}
}
#[cfg(not(feature = "u128-support"))]
mod arith_impl {
#[inline(always)]
fn split_u64(i: u64) -> (u64, u64) {
(i >> 32, i & 0xFFFFFFFF)
}
#[inline(always)]
fn combine_u64(hi: u64, lo: u64) -> u64 {
(hi << 32) | lo
}
/// Calculate a - b - borrow, returning the result and modifying
/// the borrow value.
#[inline(always)]
pub fn sbb(a: u64, b: u64, borrow: &mut u64) -> u64 {
let (a_hi, a_lo) = split_u64(a);
let (b_hi, b_lo) = split_u64(b);
let (b, r0) = split_u64((1 << 32) + a_lo - b_lo - *borrow);
let (b, r1) = split_u64((1 << 32) + a_hi - b_hi - ((b == 0) as u64));
*borrow = (b == 0) as u64;
combine_u64(r1, r0)
}
/// Calculate a + b + carry, returning the sum and modifying the
/// carry value.
#[inline(always)]
pub fn adc(a: u64, b: u64, carry: &mut u64) -> u64 {
let (a_hi, a_lo) = split_u64(a);
let (b_hi, b_lo) = split_u64(b);
let (carry_hi, carry_lo) = split_u64(*carry);
let (t, r0) = split_u64(a_lo + b_lo + carry_lo);
let (t, r1) = split_u64(t + a_hi + b_hi + carry_hi);
*carry = t;
combine_u64(r1, r0)
}
/// Calculate a + (b * c) + carry, returning the least significant digit
/// and setting carry to the most significant digit.
#[inline(always)]
pub fn mac_with_carry(a: u64, b: u64, c: u64, carry: &mut u64) -> u64 {
/*
[ b_hi | b_lo ]
[ c_hi | c_lo ] *
-------------------------------------------
[ b_lo * c_lo ] <-- w
[ b_hi * c_lo ] <-- x
[ b_lo * c_hi ] <-- y
[ b_hi * c_lo ] <-- z
[ a_hi | a_lo ]
[ C_hi | C_lo ]
*/
let (a_hi, a_lo) = split_u64(a);
let (b_hi, b_lo) = split_u64(b);
let (c_hi, c_lo) = split_u64(c);
let (carry_hi, carry_lo) = split_u64(*carry);
let (w_hi, w_lo) = split_u64(b_lo * c_lo);
let (x_hi, x_lo) = split_u64(b_hi * c_lo);
let (y_hi, y_lo) = split_u64(b_lo * c_hi);
let (z_hi, z_lo) = split_u64(b_hi * c_hi);
let (t, r0) = split_u64(w_lo + a_lo + carry_lo);
let (t, r1) = split_u64(t + w_hi + x_lo + y_lo + a_hi + carry_hi);
let (t, r2) = split_u64(t + x_hi + y_hi + z_lo);
let (_, r3) = split_u64(t + z_hi);
*carry = combine_u64(r3, r2);
combine_u64(r1, r0)
}
}