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/*
* (C) 2026 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/ctr.h>
#include <botan/assert.h>
#include <botan/internal/simd_4x32.h>
namespace Botan {
BOTAN_FN_ISA_SIMD_4X32
size_t CTR_BE::ctr_proc_bs16_ctr4_simd32(const uint8_t* in, uint8_t* out, size_t length) {
BOTAN_ASSERT_NOMSG(m_pad.size() % 64 == 0);
BOTAN_DEBUG_ASSERT(m_counter.size() == m_pad.size());
const size_t pad_size = m_pad.size();
if(length < pad_size) {
return 0;
}
const size_t ctr_blocks = m_ctr_blocks;
// Load the starting counter as big-endian 32-bit words.
// Word 3 (bytes 12-15) contains the counter value in native form.
const SIMD_4x32 starting_ctr = SIMD_4x32::load_be(m_counter.data());
const uint32_t N = static_cast<uint32_t>(ctr_blocks);
// Initialize 4 counter registers for 4-way unrolled processing
SIMD_4x32 ctr0 = starting_ctr + SIMD_4x32(0, 0, 0, N);
SIMD_4x32 ctr1 = starting_ctr + SIMD_4x32(0, 0, 0, N + 1);
SIMD_4x32 ctr2 = starting_ctr + SIMD_4x32(0, 0, 0, N + 2);
SIMD_4x32 ctr3 = starting_ctr + SIMD_4x32(0, 0, 0, N + 3);
const SIMD_4x32 inc4 = SIMD_4x32(0, 0, 0, 4);
const uint8_t* pad_buf = m_pad.data();
uint8_t* ctr_buf = m_counter.data();
const size_t ctr_block_quads = ctr_blocks / 4;
size_t processed = 0;
while(length >= pad_size) {
for(size_t i = 0; i != ctr_block_quads; ++i) {
const size_t off = i * 64;
// Store and update the counter
ctr0.store_be(ctr_buf + off);
ctr1.store_be(ctr_buf + off + 16);
ctr2.store_be(ctr_buf + off + 32);
ctr3.store_be(ctr_buf + off + 48);
ctr0 += inc4;
ctr1 += inc4;
ctr2 += inc4;
ctr3 += inc4;
// Load and XOR the pad with the input blocks
auto p0 = SIMD_4x32::load_le(pad_buf + off);
auto p1 = SIMD_4x32::load_le(pad_buf + off + 16);
auto p2 = SIMD_4x32::load_le(pad_buf + off + 32);
auto p3 = SIMD_4x32::load_le(pad_buf + off + 48);
p0 ^= SIMD_4x32::load_le(in + off);
p1 ^= SIMD_4x32::load_le(in + off + 16);
p2 ^= SIMD_4x32::load_le(in + off + 32);
p3 ^= SIMD_4x32::load_le(in + off + 48);
p0.store_le(out + off);
p1.store_le(out + off + 16);
p2.store_le(out + off + 32);
p3.store_le(out + off + 48);
}
in += pad_size;
out += pad_size;
length -= pad_size;
processed += pad_size;
// Regenerate the pad buffer
m_cipher->encrypt_n(m_counter.data(), m_pad.data(), ctr_blocks);
}
return processed;
}
} // namespace Botan