Re: [PATCH net-next v6 17/23] zinc: Curve25519 generic C implementations and selftest

Joe Perches
2018-09-25T18:38:37Z

On Tue, 2018-09-25 at 16:56 +0200, Jason A. Donenfeld wrote:
> This contains two formally verified C implementations of the Curve25519
> scalar multiplication function, one for 32-bit systems, and one for
> 64-bit systems whose compiler supports efficient 128-bit integer types.
> Not only are these implementations formally verified, but they are also
> the fastest available C implementations. They have been modified to be
> friendly to kernel space and to be generally less horrendous looking,
> but still an effort has been made to retain their formally verified
> characteristic, and so the C might look slightly unidiomatic.
[]
> diff --git a/lib/zinc/curve25519/curve25519-fiat32.h b/lib/zinc/curve25519/curve25519-fiat32.h
[]
> +static __always_inline void fe_freeze(u32 out[10], const u32 in1[10])
> +{
> + { const u32 x17 = in1[9];
> + { const u32 x18 = in1[8];
> + { const u32 x16 = in1[7];
> + { const u32 x14 = in1[6];
> + { const u32 x12 = in1[5];
> + { const u32 x10 = in1[4];
> + { const u32 x8 = in1[3];
> + { const u32 x6 = in1[2];
> + { const u32 x4 = in1[1];
> + { const u32 x2 = in1[0];
> + { u32 x20; u8/*bool*/ x21 = subborrow_u26(0x0, x2, 0x3ffffed, &x20);
> + { u32 x23; u8/*bool*/ x24 = subborrow_u25(x21, x4, 0x1ffffff, &x23);
> + { u32 x26; u8/*bool*/ x27 = subborrow_u26(x24, x6, 0x3ffffff, &x26);
> + { u32 x29; u8/*bool*/ x30 = subborrow_u25(x27, x8, 0x1ffffff, &x29);
> + { u32 x32; u8/*bool*/ x33 = subborrow_u26(x30, x10, 0x3ffffff, &x32);
> + { u32 x35; u8/*bool*/ x36 = subborrow_u25(x33, x12, 0x1ffffff, &x35);
> + { u32 x38; u8/*bool*/ x39 = subborrow_u26(x36, x14, 0x3ffffff, &x38);
> + { u32 x41; u8/*bool*/ x42 = subborrow_u25(x39, x16, 0x1ffffff, &x41);
> + { u32 x44; u8/*bool*/ x45 = subborrow_u26(x42, x18, 0x3ffffff, &x44);
> + { u32 x47; u8/*bool*/ x48 = subborrow_u25(x45, x17, 0x1ffffff, &x47);
> + { u32 x49 = cmovznz32(x48, 0x0, 0xffffffff);
> + { u32 x50 = (x49 & 0x3ffffed);
> + { u32 x52; u8/*bool*/ x53 = addcarryx_u26(0x0, x20, x50, &x52);
> + { u32 x54 = (x49 & 0x1ffffff);
> + { u32 x56; u8/*bool*/ x57 = addcarryx_u25(x53, x23, x54, &x56);
> + { u32 x58 = (x49 & 0x3ffffff);
> + { u32 x60; u8/*bool*/ x61 = addcarryx_u26(x57, x26, x58, &x60);
> + { u32 x62 = (x49 & 0x1ffffff);
> + { u32 x64; u8/*bool*/ x65 = addcarryx_u25(x61, x29, x62, &x64);
> + { u32 x66 = (x49 & 0x3ffffff);
> + { u32 x68; u8/*bool*/ x69 = addcarryx_u26(x65, x32, x66, &x68);
> + { u32 x70 = (x49 & 0x1ffffff);
> + { u32 x72; u8/*bool*/ x73 = addcarryx_u25(x69, x35, x70, &x72);
> + { u32 x74 = (x49 & 0x3ffffff);
> + { u32 x76; u8/*bool*/ x77 = addcarryx_u26(x73, x38, x74, &x76);
> + { u32 x78 = (x49 & 0x1ffffff);
> + { u32 x80; u8/*bool*/ x81 = addcarryx_u25(x77, x41, x78, &x80);
> + { u32 x82 = (x49 & 0x3ffffff);
> + { u32 x84; u8/*bool*/ x85 = addcarryx_u26(x81, x44, x82, &x84);
> + { u32 x86 = (x49 & 0x1ffffff);
> + { u32 x88; addcarryx_u25(x85, x47, x86, &x88);
> + out[0] = x52;
> + out[1] = x56;
> + out[2] = x60;
> + out[3] = x64;
> + out[4] = x68;
> + out[5] = x72;
> + out[6] = x76;
> + out[7] = x80;
> + out[8] = x84;
> + out[9] = x88;
> + }}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}
> +}

Unidiomatic might be a stretch here...

[]

and elsewhere...

> +static void fe_add_impl(u32 out[10], const u32 in1[10], const u32 in2[10])
> +{
> + { const u32 x20 = in1[9];
> + { const u32 x21 = in1[8];
> + { const u32 x19 = in1[7];
> + { const u32 x17 = in1[6];
> + { const u32 x15 = in1[5];
> + { const u32 x13 = in1[4];
> + { const u32 x11 = in1[3];
> + { const u32 x9 = in1[2];
> + { const u32 x7 = in1[1];
> + { const u32 x5 = in1[0];
> + { const u32 x38 = in2[9];
> + { const u32 x39 = in2[8];
> + { const u32 x37 = in2[7];
> + { const u32 x35 = in2[6];
> + { const u32 x33 = in2[5];
> + { const u32 x31 = in2[4];
> + { const u32 x29 = in2[3];
> + { const u32 x27 = in2[2];
> + { const u32 x25 = in2[1];
> + { const u32 x23 = in2[0];
> + out[0] = (x5 + x23);
> + out[1] = (x7 + x25);
> + out[2] = (x9 + x27);
> + out[3] = (x11 + x29);
> + out[4] = (x13 + x31);
> + out[5] = (x15 + x33);
> + out[6] = (x17 + x35);
> + out[7] = (x19 + x37);
> + out[8] = (x21 + x39);
> + out[9] = (x20 + x38);
> + }}}}}}}}}}}}}}}}}}}}
> +}

etc...