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core/crypto/chacha20: Use 128-bit/256-bit SIMD

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This commit is contained in:
Yawning Angel
2024-08-10 18:32:37 +09:00
parent 708f053fe6
commit 1f3107e693
8 changed files with 1452 additions and 461 deletions
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core/crypto/chacha20/chacha20.odin
+45 -458
View File
@@ -8,119 +8,66 @@ See:
package chacha20
import "core:bytes"
import "core:encoding/endian"
import "core:math/bits"
import "core:crypto/_chacha20"
import "core:mem"
// KEY_SIZE is the (X)ChaCha20 key size in bytes.
KEY_SIZE :: 32
KEY_SIZE :: _chacha20.KEY_SIZE
// NONCE_SIZE is the ChaCha20 nonce size in bytes.
NONCE_SIZE :: 12
NONCE_SIZE :: _chacha20.NONCE_SIZE
// XNONCE_SIZE is the XChaCha20 nonce size in bytes.
XNONCE_SIZE :: 24
@(private)
_MAX_CTR_IETF :: 0xffffffff
@(private)
_BLOCK_SIZE :: 64
@(private)
_STATE_SIZE_U32 :: 16
@(private)
_ROUNDS :: 20
@(private)
_SIGMA_0: u32 : 0x61707865
@(private)
_SIGMA_1: u32 : 0x3320646e
@(private)
_SIGMA_2: u32 : 0x79622d32
@(private)
_SIGMA_3: u32 : 0x6b206574
XNONCE_SIZE :: _chacha20.XNONCE_SIZE
// Context is a ChaCha20 or XChaCha20 instance.
Context :: struct {
_s: [_STATE_SIZE_U32]u32,
_buffer: [_BLOCK_SIZE]byte,
_off: int,
_is_ietf_flavor: bool,
_is_initialized: bool,
_state: _chacha20.Context,
_impl: Implementation,
}
// init inititializes a Context for ChaCha20 or XChaCha20 with the provided
// key and nonce.
init :: proc(ctx: ^Context, key, nonce: []byte) {
init :: proc(ctx: ^Context, key, nonce: []byte, impl := Implementation.Simd256) {
if len(key) != KEY_SIZE {
panic("crypto/chacha20: invalid ChaCha20 key size")
panic("crypto/chacha20: invalid (X)ChaCha20 key size")
}
if n_len := len(nonce); n_len != NONCE_SIZE && n_len != XNONCE_SIZE {
if l := len(nonce); l != NONCE_SIZE && l != XNONCE_SIZE {
panic("crypto/chacha20: invalid (X)ChaCha20 nonce size")
}
k, n := key, nonce
// Derive the XChaCha20 subkey and sub-nonce via HChaCha20.
init_impl(ctx, impl)
is_xchacha := len(nonce) == XNONCE_SIZE
if is_xchacha {
sub_key := ctx._buffer[:KEY_SIZE]
_hchacha20(sub_key, k, n)
sub_nonce: [NONCE_SIZE]byte
sub_key := ctx._state._buffer[:KEY_SIZE]
hchacha20(sub_key, k, n, ctx._impl)
k = sub_key
n = n[16:24]
copy(sub_nonce[4:], n[16:])
n = sub_nonce[:]
}
ctx._s[0] = _SIGMA_0
ctx._s[1] = _SIGMA_1
ctx._s[2] = _SIGMA_2
ctx._s[3] = _SIGMA_3
ctx._s[4] = endian.unchecked_get_u32le(k[0:4])
ctx._s[5] = endian.unchecked_get_u32le(k[4:8])
ctx._s[6] = endian.unchecked_get_u32le(k[8:12])
ctx._s[7] = endian.unchecked_get_u32le(k[12:16])
ctx._s[8] = endian.unchecked_get_u32le(k[16:20])
ctx._s[9] = endian.unchecked_get_u32le(k[20:24])
ctx._s[10] = endian.unchecked_get_u32le(k[24:28])
ctx._s[11] = endian.unchecked_get_u32le(k[28:32])
ctx._s[12] = 0
if !is_xchacha {
ctx._s[13] = endian.unchecked_get_u32le(n[0:4])
ctx._s[14] = endian.unchecked_get_u32le(n[4:8])
ctx._s[15] = endian.unchecked_get_u32le(n[8:12])
} else {
ctx._s[13] = 0
ctx._s[14] = endian.unchecked_get_u32le(n[0:4])
ctx._s[15] = endian.unchecked_get_u32le(n[4:8])
_chacha20.init(&ctx._state, k, n, is_xchacha)
if is_xchacha {
// The sub-key is stored in the keystream buffer. While
// this will be overwritten in most circumstances, explicitly
// clear it out early.
mem.zero_explicit(&ctx._buffer, KEY_SIZE)
mem.zero_explicit(&ctx._state._buffer, KEY_SIZE)
}
ctx._off = _BLOCK_SIZE
ctx._is_ietf_flavor = !is_xchacha
ctx._is_initialized = true
}
// seek seeks the (X)ChaCha20 stream counter to the specified block.
seek :: proc(ctx: ^Context, block_nr: u64) {
assert(ctx._is_initialized)
if ctx._is_ietf_flavor {
if block_nr > _MAX_CTR_IETF {
panic("crypto/chacha20: attempted to seek past maximum counter")
}
} else {
ctx._s[13] = u32(block_nr >> 32)
}
ctx._s[12] = u32(block_nr)
ctx._off = _BLOCK_SIZE
_chacha20.seek(&ctx._state, block_nr)
}
// xor_bytes XORs each byte in src with bytes taken from the (X)ChaCha20
// keystream, and writes the resulting output to dst. Dst and src MUST
// alias exactly or not at all.
xor_bytes :: proc(ctx: ^Context, dst, src: []byte) {
assert(ctx._is_initialized)
assert(ctx._state._is_initialized)
src, dst := src, dst
if dst_len := len(dst); dst_len < len(src) {
@@ -131,12 +78,13 @@ xor_bytes :: proc(ctx: ^Context, dst, src: []byte) {
panic("crypto/chacha20: dst and src alias inexactly")
}
for remaining := len(src); remaining > 0; {
st := &ctx._state
#no_bounds_check for remaining := len(src); remaining > 0; {
// Process multiple blocks at once
if ctx._off == _BLOCK_SIZE {
if nr_blocks := remaining / _BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _BLOCK_SIZE
_do_blocks(ctx, dst, src, nr_blocks)
if st._off == _chacha20.BLOCK_SIZE {
if nr_blocks := remaining / _chacha20.BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _chacha20.BLOCK_SIZE
stream_blocks(ctx, dst, src, nr_blocks)
remaining -= direct_bytes
if remaining == 0 {
return
@@ -147,17 +95,17 @@ xor_bytes :: proc(ctx: ^Context, dst, src: []byte) {
// If there is a partial block, generate and buffer 1 block
// worth of keystream.
_do_blocks(ctx, ctx._buffer[:], nil, 1)
ctx._off = 0
stream_blocks(ctx, st._buffer[:], nil, 1)
st._off = 0
}
// Process partial blocks from the buffered keystream.
to_xor := min(_BLOCK_SIZE - ctx._off, remaining)
buffered_keystream := ctx._buffer[ctx._off:]
to_xor := min(_chacha20.BLOCK_SIZE - st._off, remaining)
buffered_keystream := st._buffer[st._off:]
for i := 0; i < to_xor; i = i + 1 {
dst[i] = buffered_keystream[i] ~ src[i]
}
ctx._off += to_xor
st._off += to_xor
dst = dst[to_xor:]
src = src[to_xor:]
remaining -= to_xor
@@ -166,15 +114,15 @@ xor_bytes :: proc(ctx: ^Context, dst, src: []byte) {
// keystream_bytes fills dst with the raw (X)ChaCha20 keystream output.
keystream_bytes :: proc(ctx: ^Context, dst: []byte) {
assert(ctx._is_initialized)
assert(ctx._state._is_initialized)
dst := dst
for remaining := len(dst); remaining > 0; {
dst, st := dst, &ctx._state
#no_bounds_check for remaining := len(dst); remaining > 0; {
// Process multiple blocks at once
if ctx._off == _BLOCK_SIZE {
if nr_blocks := remaining / _BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _BLOCK_SIZE
_do_blocks(ctx, dst, nil, nr_blocks)
if st._off == _chacha20.BLOCK_SIZE {
if nr_blocks := remaining / _chacha20.BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _chacha20.BLOCK_SIZE
stream_blocks(ctx, dst, nil, nr_blocks)
remaining -= direct_bytes
if remaining == 0 {
return
@@ -184,15 +132,15 @@ keystream_bytes :: proc(ctx: ^Context, dst: []byte) {
// If there is a partial block, generate and buffer 1 block
// worth of keystream.
_do_blocks(ctx, ctx._buffer[:], nil, 1)
ctx._off = 0
stream_blocks(ctx, st._buffer[:], nil, 1)
st._off = 0
}
// Process partial blocks from the buffered keystream.
to_copy := min(_BLOCK_SIZE - ctx._off, remaining)
buffered_keystream := ctx._buffer[ctx._off:]
to_copy := min(_chacha20.BLOCK_SIZE - st._off, remaining)
buffered_keystream := st._buffer[st._off:]
copy(dst[:to_copy], buffered_keystream[:to_copy])
ctx._off += to_copy
st._off += to_copy
dst = dst[to_copy:]
remaining -= to_copy
}
@@ -201,366 +149,5 @@ keystream_bytes :: proc(ctx: ^Context, dst: []byte) {
// reset sanitizes the Context. The Context must be re-initialized to
// be used again.
reset :: proc(ctx: ^Context) {
mem.zero_explicit(&ctx._s, size_of(ctx._s))
mem.zero_explicit(&ctx._buffer, size_of(ctx._buffer))
ctx._is_initialized = false
}
@(private)
_do_blocks :: proc(ctx: ^Context, dst, src: []byte, nr_blocks: int) {
// Enforce the maximum consumed keystream per nonce.
//
// While all modern "standard" definitions of ChaCha20 use
// the IETF 32-bit counter, for XChaCha20 most common
// implementations allow for a 64-bit counter.
//
// Honestly, the answer here is "use a MRAE primitive", but
// go with common practice in the case of XChaCha20.
if ctx._is_ietf_flavor {
if u64(ctx._s[12]) + u64(nr_blocks) > 0xffffffff {
panic("crypto/chacha20: maximum ChaCha20 keystream per nonce reached")
}
} else {
ctr := (u64(ctx._s[13]) << 32) | u64(ctx._s[12])
if _, carry := bits.add_u64(ctr, u64(nr_blocks), 0); carry != 0 {
panic("crypto/chacha20: maximum XChaCha20 keystream per nonce reached")
}
}
dst, src := dst, src
x := &ctx._s
for n := 0; n < nr_blocks; n = n + 1 {
x0, x1, x2, x3 := _SIGMA_0, _SIGMA_1, _SIGMA_2, _SIGMA_3
x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15 := x[4], x[5], x[6], x[7], x[8], x[9], x[10], x[11], x[12], x[13], x[14], x[15]
for i := _ROUNDS; i > 0; i = i - 2 {
// Even when forcing inlining manually inlining all of
// these is decently faster.
// quarterround(x, 0, 4, 8, 12)
x0 += x4
x12 ~= x0
x12 = bits.rotate_left32(x12, 16)
x8 += x12
x4 ~= x8
x4 = bits.rotate_left32(x4, 12)
x0 += x4
x12 ~= x0
x12 = bits.rotate_left32(x12, 8)
x8 += x12
x4 ~= x8
x4 = bits.rotate_left32(x4, 7)
// quarterround(x, 1, 5, 9, 13)
x1 += x5
x13 ~= x1
x13 = bits.rotate_left32(x13, 16)
x9 += x13
x5 ~= x9
x5 = bits.rotate_left32(x5, 12)
x1 += x5
x13 ~= x1
x13 = bits.rotate_left32(x13, 8)
x9 += x13
x5 ~= x9
x5 = bits.rotate_left32(x5, 7)
// quarterround(x, 2, 6, 10, 14)
x2 += x6
x14 ~= x2
x14 = bits.rotate_left32(x14, 16)
x10 += x14
x6 ~= x10
x6 = bits.rotate_left32(x6, 12)
x2 += x6
x14 ~= x2
x14 = bits.rotate_left32(x14, 8)
x10 += x14
x6 ~= x10
x6 = bits.rotate_left32(x6, 7)
// quarterround(x, 3, 7, 11, 15)
x3 += x7
x15 ~= x3
x15 = bits.rotate_left32(x15, 16)
x11 += x15
x7 ~= x11
x7 = bits.rotate_left32(x7, 12)
x3 += x7
x15 ~= x3
x15 = bits.rotate_left32(x15, 8)
x11 += x15
x7 ~= x11
x7 = bits.rotate_left32(x7, 7)
// quarterround(x, 0, 5, 10, 15)
x0 += x5
x15 ~= x0
x15 = bits.rotate_left32(x15, 16)
x10 += x15
x5 ~= x10
x5 = bits.rotate_left32(x5, 12)
x0 += x5
x15 ~= x0
x15 = bits.rotate_left32(x15, 8)
x10 += x15
x5 ~= x10
x5 = bits.rotate_left32(x5, 7)
// quarterround(x, 1, 6, 11, 12)
x1 += x6
x12 ~= x1
x12 = bits.rotate_left32(x12, 16)
x11 += x12
x6 ~= x11
x6 = bits.rotate_left32(x6, 12)
x1 += x6
x12 ~= x1
x12 = bits.rotate_left32(x12, 8)
x11 += x12
x6 ~= x11
x6 = bits.rotate_left32(x6, 7)
// quarterround(x, 2, 7, 8, 13)
x2 += x7
x13 ~= x2
x13 = bits.rotate_left32(x13, 16)
x8 += x13
x7 ~= x8
x7 = bits.rotate_left32(x7, 12)
x2 += x7
x13 ~= x2
x13 = bits.rotate_left32(x13, 8)
x8 += x13
x7 ~= x8
x7 = bits.rotate_left32(x7, 7)
// quarterround(x, 3, 4, 9, 14)
x3 += x4
x14 ~= x3
x14 = bits.rotate_left32(x14, 16)
x9 += x14
x4 ~= x9
x4 = bits.rotate_left32(x4, 12)
x3 += x4
x14 ~= x3
x14 = bits.rotate_left32(x14, 8)
x9 += x14
x4 ~= x9
x4 = bits.rotate_left32(x4, 7)
}
x0 += _SIGMA_0
x1 += _SIGMA_1
x2 += _SIGMA_2
x3 += _SIGMA_3
x4 += x[4]
x5 += x[5]
x6 += x[6]
x7 += x[7]
x8 += x[8]
x9 += x[9]
x10 += x[10]
x11 += x[11]
x12 += x[12]
x13 += x[13]
x14 += x[14]
x15 += x[15]
// While the "correct" answer to getting more performance out of
// this is "use vector operations", support for that is currently
// a work in progress/to be designed.
//
// In the meantime:
// - The caller(s) ensure that src/dst are valid.
// - The compiler knows if the target is picky about alignment.
#no_bounds_check {
if src != nil {
endian.unchecked_put_u32le(dst[0:4], endian.unchecked_get_u32le(src[0:4]) ~ x0)
endian.unchecked_put_u32le(dst[4:8], endian.unchecked_get_u32le(src[4:8]) ~ x1)
endian.unchecked_put_u32le(dst[8:12], endian.unchecked_get_u32le(src[8:12]) ~ x2)
endian.unchecked_put_u32le(dst[12:16], endian.unchecked_get_u32le(src[12:16]) ~ x3)
endian.unchecked_put_u32le(dst[16:20], endian.unchecked_get_u32le(src[16:20]) ~ x4)
endian.unchecked_put_u32le(dst[20:24], endian.unchecked_get_u32le(src[20:24]) ~ x5)
endian.unchecked_put_u32le(dst[24:28], endian.unchecked_get_u32le(src[24:28]) ~ x6)
endian.unchecked_put_u32le(dst[28:32], endian.unchecked_get_u32le(src[28:32]) ~ x7)
endian.unchecked_put_u32le(dst[32:36], endian.unchecked_get_u32le(src[32:36]) ~ x8)
endian.unchecked_put_u32le(dst[36:40], endian.unchecked_get_u32le(src[36:40]) ~ x9)
endian.unchecked_put_u32le(dst[40:44], endian.unchecked_get_u32le(src[40:44]) ~ x10)
endian.unchecked_put_u32le(dst[44:48], endian.unchecked_get_u32le(src[44:48]) ~ x11)
endian.unchecked_put_u32le(dst[48:52], endian.unchecked_get_u32le(src[48:52]) ~ x12)
endian.unchecked_put_u32le(dst[52:56], endian.unchecked_get_u32le(src[52:56]) ~ x13)
endian.unchecked_put_u32le(dst[56:60], endian.unchecked_get_u32le(src[56:60]) ~ x14)
endian.unchecked_put_u32le(dst[60:64], endian.unchecked_get_u32le(src[60:64]) ~ x15)
src = src[_BLOCK_SIZE:]
} else {
endian.unchecked_put_u32le(dst[0:4], x0)
endian.unchecked_put_u32le(dst[4:8], x1)
endian.unchecked_put_u32le(dst[8:12], x2)
endian.unchecked_put_u32le(dst[12:16], x3)
endian.unchecked_put_u32le(dst[16:20], x4)
endian.unchecked_put_u32le(dst[20:24], x5)
endian.unchecked_put_u32le(dst[24:28], x6)
endian.unchecked_put_u32le(dst[28:32], x7)
endian.unchecked_put_u32le(dst[32:36], x8)
endian.unchecked_put_u32le(dst[36:40], x9)
endian.unchecked_put_u32le(dst[40:44], x10)
endian.unchecked_put_u32le(dst[44:48], x11)
endian.unchecked_put_u32le(dst[48:52], x12)
endian.unchecked_put_u32le(dst[52:56], x13)
endian.unchecked_put_u32le(dst[56:60], x14)
endian.unchecked_put_u32le(dst[60:64], x15)
}
dst = dst[_BLOCK_SIZE:]
}
// Increment the counter. Overflow checking is done upon
// entry into the routine, so a 64-bit increment safely
// covers both cases.
new_ctr := ((u64(ctx._s[13]) << 32) | u64(ctx._s[12])) + 1
x[12] = u32(new_ctr)
x[13] = u32(new_ctr >> 32)
}
}
@(private)
_hchacha20 :: proc "contextless" (dst, key, nonce: []byte) {
x0, x1, x2, x3 := _SIGMA_0, _SIGMA_1, _SIGMA_2, _SIGMA_3
x4 := endian.unchecked_get_u32le(key[0:4])
x5 := endian.unchecked_get_u32le(key[4:8])
x6 := endian.unchecked_get_u32le(key[8:12])
x7 := endian.unchecked_get_u32le(key[12:16])
x8 := endian.unchecked_get_u32le(key[16:20])
x9 := endian.unchecked_get_u32le(key[20:24])
x10 := endian.unchecked_get_u32le(key[24:28])
x11 := endian.unchecked_get_u32le(key[28:32])
x12 := endian.unchecked_get_u32le(nonce[0:4])
x13 := endian.unchecked_get_u32le(nonce[4:8])
x14 := endian.unchecked_get_u32le(nonce[8:12])
x15 := endian.unchecked_get_u32le(nonce[12:16])
for i := _ROUNDS; i > 0; i = i - 2 {
// quarterround(x, 0, 4, 8, 12)
x0 += x4
x12 ~= x0
x12 = bits.rotate_left32(x12, 16)
x8 += x12
x4 ~= x8
x4 = bits.rotate_left32(x4, 12)
x0 += x4
x12 ~= x0
x12 = bits.rotate_left32(x12, 8)
x8 += x12
x4 ~= x8
x4 = bits.rotate_left32(x4, 7)
// quarterround(x, 1, 5, 9, 13)
x1 += x5
x13 ~= x1
x13 = bits.rotate_left32(x13, 16)
x9 += x13
x5 ~= x9
x5 = bits.rotate_left32(x5, 12)
x1 += x5
x13 ~= x1
x13 = bits.rotate_left32(x13, 8)
x9 += x13
x5 ~= x9
x5 = bits.rotate_left32(x5, 7)
// quarterround(x, 2, 6, 10, 14)
x2 += x6
x14 ~= x2
x14 = bits.rotate_left32(x14, 16)
x10 += x14
x6 ~= x10
x6 = bits.rotate_left32(x6, 12)
x2 += x6
x14 ~= x2
x14 = bits.rotate_left32(x14, 8)
x10 += x14
x6 ~= x10
x6 = bits.rotate_left32(x6, 7)
// quarterround(x, 3, 7, 11, 15)
x3 += x7
x15 ~= x3
x15 = bits.rotate_left32(x15, 16)
x11 += x15
x7 ~= x11
x7 = bits.rotate_left32(x7, 12)
x3 += x7
x15 ~= x3
x15 = bits.rotate_left32(x15, 8)
x11 += x15
x7 ~= x11
x7 = bits.rotate_left32(x7, 7)
// quarterround(x, 0, 5, 10, 15)
x0 += x5
x15 ~= x0
x15 = bits.rotate_left32(x15, 16)
x10 += x15
x5 ~= x10
x5 = bits.rotate_left32(x5, 12)
x0 += x5
x15 ~= x0
x15 = bits.rotate_left32(x15, 8)
x10 += x15
x5 ~= x10
x5 = bits.rotate_left32(x5, 7)
// quarterround(x, 1, 6, 11, 12)
x1 += x6
x12 ~= x1
x12 = bits.rotate_left32(x12, 16)
x11 += x12
x6 ~= x11
x6 = bits.rotate_left32(x6, 12)
x1 += x6
x12 ~= x1
x12 = bits.rotate_left32(x12, 8)
x11 += x12
x6 ~= x11
x6 = bits.rotate_left32(x6, 7)
// quarterround(x, 2, 7, 8, 13)
x2 += x7
x13 ~= x2
x13 = bits.rotate_left32(x13, 16)
x8 += x13
x7 ~= x8
x7 = bits.rotate_left32(x7, 12)
x2 += x7
x13 ~= x2
x13 = bits.rotate_left32(x13, 8)
x8 += x13
x7 ~= x8
x7 = bits.rotate_left32(x7, 7)
// quarterround(x, 3, 4, 9, 14)
x3 += x4
x14 ~= x3
x14 = bits.rotate_left32(x14, 16)
x9 += x14
x4 ~= x9
x4 = bits.rotate_left32(x4, 12)
x3 += x4
x14 ~= x3
x14 = bits.rotate_left32(x14, 8)
x9 += x14
x4 ~= x9
x4 = bits.rotate_left32(x4, 7)
}
endian.unchecked_put_u32le(dst[0:4], x0)
endian.unchecked_put_u32le(dst[4:8], x1)
endian.unchecked_put_u32le(dst[8:12], x2)
endian.unchecked_put_u32le(dst[12:16], x3)
endian.unchecked_put_u32le(dst[16:20], x12)
endian.unchecked_put_u32le(dst[20:24], x13)
endian.unchecked_put_u32le(dst[24:28], x14)
endian.unchecked_put_u32le(dst[28:32], x15)
_chacha20.reset(&ctx._state)
}
core/crypto/chacha20/chacha20_impl.odin
+52
View File
@@ -0,0 +1,52 @@
package chacha20
import "base:intrinsics"
import "core:crypto/_chacha20/ref"
import "core:crypto/_chacha20/simd128"
import "core:crypto/_chacha20/simd256"
// Implementation is a ChaCha20 implementation. Most callers will not need
// to use this as the package will automatically select the most performant
// implementation available.
Implementation :: enum {
Portable,
Simd128,
Simd256,
}
@(private)
init_impl :: proc(ctx: ^Context, impl: Implementation) {
impl := impl
if impl == .Simd256 && !simd256.is_performant() {
impl = .Simd128
}
if impl == .Simd128 && !simd128.is_performant() {
impl = .Portable
}
ctx._impl = impl
}
@(private)
stream_blocks :: proc(ctx: ^Context, dst, src: []byte, nr_blocks: int) {
switch ctx._impl {
case .Simd256:
simd256.stream_blocks(&ctx._state, dst, src, nr_blocks)
case .Simd128:
simd128.stream_blocks(&ctx._state, dst, src, nr_blocks)
case .Portable:
ref.stream_blocks(&ctx._state, dst, src, nr_blocks)
}
}
@(private)
hchacha20 :: proc "contextless" (dst, key, nonce: []byte, impl: Implementation) {
switch impl {
case .Simd256:
simd256.hchacha20(dst, key, nonce)
case .Simd128:
simd128.hchacha20(dst, key, nonce)
case .Portable:
ref.hchacha20(dst, key, nonce)
}
}