AVX2: enc: unroll inner loop

lib/arch/avx2/enc_loop.c

@@ -1,3 +1,37 @@
+static inline void
+enc_loop_avx2_inner_first (const uint8_t **s, uint8_t **o)
+{
+	// First load is done at s - 0 to not get a segfault:
+	__m256i src = _mm256_loadu_si256((__m256i *) *s);
+
+	// Shift by 4 bytes, as required by enc_reshuffle:
+	src = _mm256_permutevar8x32_epi32(src, _mm256_setr_epi32(0, 0, 1, 2, 3, 4, 5, 6));
+
+	// Reshuffle, translate, store:
+	src = enc_reshuffle(src);
+	src = enc_translate(src);
+	_mm256_storeu_si256((__m256i *) *o, src);
+
+	// Subsequent loads will be done at s - 4, set pointer for next round:
+	*s += 20;
+	*o += 32;
+}
+
+static inline void
+enc_loop_avx2_inner (const uint8_t **s, uint8_t **o)
+{
+	// Load input:
+	__m256i src = _mm256_loadu_si256((__m256i *) *s);
+
+	// Reshuffle, translate, store:
+	src = enc_reshuffle(src);
+	src = enc_translate(src);
+	_mm256_storeu_si256((__m256i *) *o, src);
+
+	*s += 24;
+	*o += 32;
+}
+
 static inline void
 enc_loop_avx2 (const uint8_t **s, size_t *slen, uint8_t **o, size_t *olen)
 {
@@ -14,30 +48,40 @@ enc_loop_avx2 (const uint8_t **s, size_t *slen, uint8_t **o, size_t *olen)
 	*slen -= rounds * 24;   // 24 bytes consumed per round
 	*olen += rounds * 32;   // 32 bytes produced per round
 
-	// First load is done at s - 0 to not get a segfault:
-	__m256i inputvector = _mm256_loadu_si256((__m256i *) *s);
-
-	// Subsequent loads will be done at s - 4, set pointer for next round:
-	*s += 20;
-
-	// Shift by 4 bytes, as required by enc_reshuffle:
-	inputvector = _mm256_permutevar8x32_epi32(inputvector, _mm256_setr_epi32(0, 0, 1, 2, 3, 4, 5, 6));
-
-	for (;;) {
-
-		// Reshuffle, translate, store:
-		inputvector = enc_reshuffle(inputvector);
-		inputvector = enc_translate(inputvector);
-		_mm256_storeu_si256((__m256i *) *o, inputvector);
-		*o += 32;
+	// The first loop iteration requires special handling to ensure that
+	// the read, which is done at an offset, does not underflow the buffer:
+	enc_loop_avx2_inner_first(s, o);
+	rounds--;
 
-		if (--rounds == 0) {
-			break;
+	while (rounds > 0) {
+		if (rounds >= 8) {
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			rounds -= 8;
+			continue;
 		}
-
-		// Load for the next round:
-		inputvector = _mm256_loadu_si256((__m256i *) *s);
-		*s += 24;
+		if (rounds >= 4) {
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			rounds -= 4;
+			continue;
+		}
+		if (rounds >= 2) {
+			enc_loop_avx2_inner(s, o);
+			enc_loop_avx2_inner(s, o);
+			rounds -= 2;
+			continue;
+		}
+		enc_loop_avx2_inner(s, o);
+		break;
 	}
 
 	// Add the offset back: