On Sat, Oct 20, 2018 at 11:06:00PM +0800, Ard Biesheuvel wrote: > >> > + > >> > +#define NH_STRIDE(K0, K1, K2, K3) \ > >> > +({ \ > >> > + m_A = get_unaligned_le32(src); src += 4; \ > >> > + m_B = get_unaligned_le32(src); src += 4; \ > >> > + m_C = get_unaligned_le32(src); src += 4; \ > >> > + m_D = get_unaligned_le32(src); src += 4; \ > >> > + K3##_A = *key++; \ > >> > + K3##_B = *key++; \ > >> > + K3##_C = *key++; \ > >> > + K3##_D = *key++; \ > >> > + sum0 += (u64)(u32)(m_A + K0##_A) * (u32)(m_C + K0##_C); \ > >> > + sum1 += (u64)(u32)(m_A + K1##_A) * (u32)(m_C + K1##_C); \ > >> > + sum2 += (u64)(u32)(m_A + K2##_A) * (u32)(m_C + K2##_C); \ > >> > + sum3 += (u64)(u32)(m_A + K3##_A) * (u32)(m_C + K3##_C); \ > >> > + sum0 += (u64)(u32)(m_B + K0##_B) * (u32)(m_D + K0##_D); \ > >> > + sum1 += (u64)(u32)(m_B + K1##_B) * (u32)(m_D + K1##_D); \ > >> > + sum2 += (u64)(u32)(m_B + K2##_B) * (u32)(m_D + K2##_D); \ > >> > + sum3 += (u64)(u32)(m_B + K3##_B) * (u32)(m_D + K3##_D); \ > >> > +}) > >> > + > >> > +static void nh_generic(const u32 *key, const u8 *src, size_t srclen, > >> > + __le64 hash[NH_NUM_PASSES]) > >> > +{ > >> > + u64 sum0 = 0, sum1 = 0, sum2 = 0, sum3 = 0; > >> > + u32 k0_A = *key++; > >> > + u32 k0_B = *key++; > >> > + u32 k0_C = *key++; > >> > + u32 k0_D = *key++; > >> > + u32 k1_A = *key++; > >> > + u32 k1_B = *key++; > >> > + u32 k1_C = *key++; > >> > + u32 k1_D = *key++; > >> > + u32 k2_A = *key++; > >> > + u32 k2_B = *key++; > >> > + u32 k2_C = *key++; > >> > + u32 k2_D = *key++; > >> > + u32 k3_A, k3_B, k3_C, k3_D; > >> > + u32 m_A, m_B, m_C, m_D; > >> > + size_t n = srclen / NH_MESSAGE_UNIT; > >> > + > >> > + BUILD_BUG_ON(NH_PAIR_STRIDE != 2); > >> > + BUILD_BUG_ON(NH_NUM_PASSES != 4); > >> > + > >> > + while (n >= 4) { > >> > + NH_STRIDE(k0, k1, k2, k3); > >> > + NH_STRIDE(k1, k2, k3, k0); > >> > + NH_STRIDE(k2, k3, k0, k1); > >> > + NH_STRIDE(k3, k0, k1, k2); > >> > + n -= 4; > >> > + } > >> > + if (n) { > >> > + NH_STRIDE(k0, k1, k2, k3); > >> > + if (--n) { > >> > + NH_STRIDE(k1, k2, k3, k0); > >> > + if (--n) > >> > + NH_STRIDE(k2, k3, k0, k1); > >> > + } > >> > + } > >> > + > >> > >> This all looks a bit clunky to me, with the macro, the *key++s in the > >> initializers and these conditionals. > >> > >> Was it written in this particular way to get GCC to optimize it in the > >> right way? > > > > This does get compiled into something much faster than a naive version, which > > you can find commented out at > > https://github.com/google/adiantum/blob/master/benchmark/src/nh.c#L14. > > > > Though, I admit that I haven't put a ton of effort into this C implementation of > > NH yet. Right now it's actually somewhat of a translation of the NEON version. > > I'll do some experiments and see if it can be made into something less ugly > > without losing performance. > > > > No that's fine but please document it. > Hmm, I'm actually leaning towards the following instead. Unrolling multiple strides to try to reduce loads of the keys doesn't seem worthwhile in the C implementation; for one, it bloats the code size a lot (412 => 2332 bytes on arm32). static void nh_generic(const u32 *key, const u8 *message, size_t message_len, __le64 hash[NH_NUM_PASSES]) { u64 sums[4] = { 0, 0, 0, 0 }; BUILD_BUG_ON(NH_PAIR_STRIDE != 2); BUILD_BUG_ON(NH_NUM_PASSES != 4); while (message_len) { u32 m0 = get_unaligned_le32(message + 0); u32 m1 = get_unaligned_le32(message + 4); u32 m2 = get_unaligned_le32(message + 8); u32 m3 = get_unaligned_le32(message + 12); sums[0] += (u64)(u32)(m0 + key[ 0]) * (u32)(m2 + key[ 2]); sums[1] += (u64)(u32)(m0 + key[ 4]) * (u32)(m2 + key[ 6]); sums[2] += (u64)(u32)(m0 + key[ 8]) * (u32)(m2 + key[10]); sums[3] += (u64)(u32)(m0 + key[12]) * (u32)(m2 + key[14]); sums[0] += (u64)(u32)(m1 + key[ 1]) * (u32)(m3 + key[ 3]); sums[1] += (u64)(u32)(m1 + key[ 5]) * (u32)(m3 + key[ 7]); sums[2] += (u64)(u32)(m1 + key[ 9]) * (u32)(m3 + key[11]); sums[3] += (u64)(u32)(m1 + key[13]) * (u32)(m3 + key[15]); key += NH_MESSAGE_UNIT / sizeof(key[0]); message += NH_MESSAGE_UNIT; message_len -= NH_MESSAGE_UNIT; } hash[0] = cpu_to_le64(sums[0]); hash[1] = cpu_to_le64(sums[1]); hash[2] = cpu_to_le64(sums[2]); hash[3] = cpu_to_le64(sums[3]); }
![]() |