1use crate::prelude::*;
 2use algebra::Field;
 3use r1cs_core::SynthesisError;
 4
 5/// Generates constraints for selecting between one of two values.
 6pub trait CondSelectGadget<ConstraintF: Field>
 7where
 8    Self: Sized,
 9{
10    /// If `cond == &Boolean::TRUE`, then this returns `true_value`; else, returns `false_value`.
11    ///
12    /// # Note
13    /// `Self::conditionally_select(cond, true_value, false_value)?` can be more succinctly written as
14    /// `cond.select(&true_value, &false_value)?`.
15    fn conditionally_select(
16        cond: &Boolean<ConstraintF>,
17        true_value: &Self,
18        false_value: &Self,
19    ) -> Result<Self, SynthesisError>;
20}
21
22/// Performs a lookup in a 4-element table using two bits.
23pub trait TwoBitLookupGadget<ConstraintF: Field>
24where
25    Self: Sized,
26{
27    /// The type of values being looked up.
28    type TableConstant;
29
30    /// Interprets the slice `bits` as a two-bit integer `b = bits[0] + (bits[1] << 1)`,
31    /// and then outputs `constants[b]`.
32    ///
33    /// For example, if `bits == [0, 1]`, and `constants == [0, 1, 2, 3]`, this method
34    /// should output a variable corresponding to `2`.
35    ///
36    /// # Panics
37    ///
38    /// This method panics if `bits.len() != 2` or `constants.len() != 4`.
39    fn two_bit_lookup(
40        bits: &[Boolean<ConstraintF>],
41        constants: &[Self::TableConstant],
42    ) -> Result<Self, SynthesisError>;
43}
44
45/// Uses three bits to perform a lookup into a table, where the last bit
46/// conditionally negates the looked-up value.
47pub trait ThreeBitCondNegLookupGadget<ConstraintF: Field>
48where
49    Self: Sized,
50{
51    /// The type of values being looked up.
52    type TableConstant;
53
54    /// Interprets the slice `bits` as a two-bit integer `b = bits[0] + (bits[1] << 1)`,
55    /// and then outputs `constants[b] * c`, where `c = if bits[2] { -1 } else { 1 };`.
56    ///
57    /// That is, `bits[2]` conditionally negates the looked-up value.
58    ///
59    /// For example, if `bits == [1, 0, 1]`, and `constants == [0, 1, 2, 3]`, this method
60    /// should output a variable corresponding to `-1`.
61    ///
62    /// # Panics
63    ///
64    /// This method panics if `bits.len() != 3` or `constants.len() != 4`.
65    fn three_bit_cond_neg_lookup(
66        bits: &[Boolean<ConstraintF>],
67        b0b1: &Boolean<ConstraintF>,
68        constants: &[Self::TableConstant],
69    ) -> Result<Self, SynthesisError>;
70}