fiat-constify: Fix implementation for fiat-crypto >= 0.0.21

[MasterAwesome]

fiat-crypto introduced new types instead of just type aliases, this causes the generated code to no longer compile. This is a breaking change since this will no longer compile code generated by fiat-crypto version < 0.0.21

Tests:

• All fiat-crypto rust crate can be compiled using rustc

Codegen

Multiple output args

Before

#[inline]
pub fn fiat_p224_divstep(out1: &mut u64, out2: &mut [u64; 5], out3: &mut [u64; 5], out4: &mut [u64; 4], out5: &mut [u64; 4], arg1: u64, arg2: &[u64; 5], arg3: &[u64; 5], arg4: &[u64; 4], arg5: &[u64; 4]) {
  // <snipped>
  *out1 = x112;
  out2[0] = x7;
  out2[1] = x8;
  out2[2] = x9;
  out2[3] = x10;
  out2[4] = x11;
  out3[0] = x114;
  out3[1] = x115;
  out3[2] = x116;
  out3[3] = x117;
  out3[4] = x118;
  out4[0] = x119;
  out4[1] = x120;
  out4[2] = x121;
  out4[3] = x122;
  out5[0] = x123;
  out5[1] = x124;
  out5[2] = x125;
  out5[3] = x126;
}

After

#[inline]
pub const fn fiat_p224_divstep(
    arg1: u64,
    arg2: &[u64; 5],
    arg3: &[u64; 5],
    arg4: &[u64; 4],
    arg5: &[u64; 4],
) -> (u64, [u64; 5], [u64; 5], [u64; 4], [u64; 4]) {
    // <snipped> 
    (
        x112,
        [x7, x8, x9, x10, x11],
        [x114, x115, x116, x117, x118],
        [x119, x120, x121, x122],
        [x123, x124, x125, x126],
    )
}

Newtyped const output/input

Before

pub fn fiat_p521_relax(out1: &mut fiat_p521_loose_field_element, arg1: &fiat_p521_tight_field_element) {
  let x1: u64 = (arg1[0]);
  let x2: u64 = (arg1[1]);
  let x3: u64 = (arg1[2]);
  let x4: u64 = (arg1[3]);
  let x5: u64 = (arg1[4]);
  let x6: u64 = (arg1[5]);
  let x7: u64 = (arg1[6]);
  let x8: u64 = (arg1[7]);
  let x9: u64 = (arg1[8]);
  out1[0] = x1;
  out1[1] = x2;
  out1[2] = x3;
  out1[3] = x4;
  out1[4] = x5;
  out1[5] = x6;
  out1[6] = x7;
  out1[7] = x8;
  out1[8] = x9;
}

After

pub const fn fiat_p521_relax(
    arg1: &fiat_p521_tight_field_element,
) -> fiat_p521_loose_field_element {
    let arg1 = &arg1.0;
    let x1: u64 = (arg1[0]);
    let x2: u64 = (arg1[1]);
    let x3: u64 = (arg1[2]);
    let x4: u64 = (arg1[3]);
    let x5: u64 = (arg1[4]);
    let x6: u64 = (arg1[5]);
    let x7: u64 = (arg1[6]);
    let x8: u64 = (arg1[7]);
    let x9: u64 = (arg1[8]);
    (fiat_p521_loose_field_element([x1, x2, x3, x4, x5, x6, x7, x8, x9]))
}

Cloned from #978
CC @tarcieri

[tarcieri]

With RustCrypto/elliptic-curves#1003 passing I'd say this is good to merge if you're finished

[MasterAwesome]

Yep I'm done with this change. Are there existing benchmarks for p521 I can check to ensure no regressions?

[tarcieri]

Hmm, doesn't look like it, but you can probably just copy the ones from e.g. p384 over