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easyxs/README.md  view on Meta::CPAN

## SV “Typing”

Perl scalars are supposed to be “untyped”, at least insofar as
strings/numbers. When conversing with other languages, though, or
serializing it’s usually helpful to break things down in greater
detail.

EasyXS defines an `exs_sv_type` macro that takes an SV as argument
and returns a member of `enum exs_sv_type_e` (typedef’d as just
`exs_sv_type_e`; see `easyxs_scalar.h` for values). The logic is compatible
with the serialization logic formulated during Perl 5.36’s development cycle.

## SV/Number Conversion

### `UV* exs_SvUV(SV* sv)`

Like `SvUV`, but if the SV’s content can’t be a UV
(e.g., the IV is negative, or the string has non-numeric characters)
an exception is thrown.

## SV/String Conversion

wireguard-tools/src/curve25519-fiat32.h  view on Meta::CPAN

		 *   to_xz (r*P)     === if swap then (x3, z3) else (x2, z2)
		 *   to_xz ((r+1)*P) === if swap then (x2, z2) else (x3, z3)
		 *   x1 is the nonzero x coordinate of the nonzero
		 *   point (r*P-(r+1)*P)
		 */
		unsigned b = 1 & (e[pos / 8] >> (pos & 7));
		swap ^= b;
		fe_cswap(&x2, &x3, swap);
		fe_cswap(&z2, &z3, swap);
		swap = b;
		/* Coq transcription of ladderstep formula (called from
		 * transcribed loop):
		 * <https://github.com/mit-plv/fiat-crypto/blob/2456d821825521f7e03e65882cc3521795b0320f/src/Curves/Montgomery/XZ.v#L89>
		 * <https://github.com/mit-plv/fiat-crypto/blob/2456d821825521f7e03e65882cc3521795b0320f/src/Curves/Montgomery/XZProofs.v#L131>
		 * x1 != 0 <https://github.com/mit-plv/fiat-crypto/blob/2456d821825521f7e03e65882cc3521795b0320f/src/Curves/Montgomery/XZProofs.v#L217>
		 * x1  = 0 <https://github.com/mit-plv/fiat-crypto/blob/2456d821825521f7e03e65882cc3521795b0320f/src/Curves/Montgomery/XZProofs.v#L147>
		 */
		fe_sub(&tmp0l, &x3, &z3);
		fe_sub(&tmp1l, &x2, &z2);
		fe_add(&x2l, &x2, &z2);
		fe_add(&z2l, &x3, &z3);