Hojun-Cho
fdd87e56bf
Subset port of ref/hare/crypto/math/bits.ha: the 32-bit rotations sha256's message schedule and compression need. The wider bits.ha surface (rotl64/rotr64, the constant-time compare family, xor) lands as callers arrive. rotr32 is exercised end-to-end by the sha256 NIST digest vectors, so no standalone @test ships here.
28 lines
1.2 KiB
Plaintext
28 lines
1.2 KiB
Plaintext
// crypto/math — bit-rotation helpers for crypto primitives. Subset port
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// of ref/hare/crypto/math/bits.ha: the 32-bit rotations sha256 needs.
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//
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// The wider bits.ha surface (rotl64/rotr64, the constant-time compare
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// family — eqslice/equ32/gtu32/…, xor, mul) lands as callers arrive;
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// only rotl32/rotr32 are pulled in for crypto/sha256. rotr32 is
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// exercised end-to-end by the sha256 NIST digest vectors (the message
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// schedule and compression both lean on it), so no standalone @test is
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// shipped here — the digest is the stronger oracle.
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package math;
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// rotl32 — rotate `x` left by `k` bits. `k` may be negative to rotate
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// right instead; see [[rotr32]]. ref/hare/crypto/math/bits.ha:9.
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// Hare's `const` locals are `let` (ww has no `const`). `int` is an 8B
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// machine word here vs Hare's 4B; the `k: u32` truncation makes the
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// width difference invisible to the masked shift count.
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export fn rotl32(x: u32, k: int) u32 = {
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let n: u32 = 32u32;
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let s: u32 = (k: u32) & (n - 1u32);
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return x << s | x >> (n - s);
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};
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// rotr32 — rotate `x` right by `k` bits. `k` may be negative to rotate
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// left instead; see [[rotl32]]. ref/hare/crypto/math/bits.ha:17.
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export fn rotr32(x: u32, k: int) u32 = {
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return rotl32(x, -k);
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};
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