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scalar: restrict split_lambda args, improve doc and VERIFY_CHECKs

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VERIFY_CHECK(r1 != r2) is added because otherwise the verify_scalar_split fails.
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Jonas Nick
2023-01-04 11:21:04 +00:00
parent 7f49aa7f2d
commit eb6bebaee3
2 changed files with 10 additions and 5 deletions
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7
src/scalar.h
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@@ -88,9 +88,10 @@ static int secp256k1_scalar_eq(const secp256k1_scalar *a, const secp256k1_scalar
/** Find r1 and r2 such that r1+r2*2^128 = k. */
static void secp256k1_scalar_split_128(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k);
/** Find r1 and r2 such that r1+r2*lambda = k,
* where r1 and r2 or their negations are maximum 128 bits long (see secp256k1_ge_mul_lambda). */
static void secp256k1_scalar_split_lambda(secp256k1_scalar *r1, secp256k1_scalar *r2, const secp256k1_scalar *k);
/** Find r1 and r2 such that r1+r2*lambda = k, where r1 and r2 or their
* negations are maximum 128 bits long (see secp256k1_ge_mul_lambda). It is
* required that r1, r2, and k all point to different objects. */
static void secp256k1_scalar_split_lambda(secp256k1_scalar * SECP256K1_RESTRICT r1, secp256k1_scalar * SECP256K1_RESTRICT r2, const secp256k1_scalar * SECP256K1_RESTRICT k);
/** Multiply a and b (without taking the modulus!), divide by 2**shift, and round to the nearest integer. Shift must be at least 256. */
static void secp256k1_scalar_mul_shift_var(secp256k1_scalar *r, const secp256k1_scalar *a, const secp256k1_scalar *b, unsigned int shift);