[Tarantool-patches] [PATCH v6 2/2] base64: improve decoder performance

[Sergey Nikiforov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Unnecessary checks were removed from internal loops.
Benchmark shows that performance is now ~1.19 times higher
(release build, Intel Core I7-9700K, only one thread).
---

Branch: https://github.com/tarantool/tarantool/tree/void234/gh-3069-fix-base64-memory-overrun-v6

 third_party/base64.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/third_party/base64.c b/third_party/base64.c
index 3ecd0843a..74260971b 100644
--- a/third_party/base64.c
+++ b/third_party/base64.c
@@ -258,10 +258,10 @@ base64_decode_block(const char *in_base64, int in_len,
 		{
 	case step_a:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_a;
-					state->result = curr_byte;
+					/* curr_byte is useless now. */
 					return out_pos - out_bin;
 				}
 				fragment = base64_decode_value(*in_pos++);
@@ -269,7 +269,7 @@ base64_decode_block(const char *in_base64, int in_len,
 			curr_byte = (fragment & 0x03f) << 2;
 	case step_b:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_b;
 					state->result = curr_byte;
@@ -277,14 +277,19 @@ base64_decode_block(const char *in_base64, int in_len,
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
+			if (out_pos >= out_end)
+			{
+				/* We are losing some data. */
+				state->step = step_b;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 			curr_byte |= (fragment & 0x030) >> 4;
 			*out_pos++ = curr_byte;
 			curr_byte = (fragment & 0x00f) << 4;
-			if (out_pos < out_end)
-				*out_pos = curr_byte;
 	case step_c:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_c;
 					state->result = curr_byte;
@@ -292,14 +297,19 @@ base64_decode_block(const char *in_base64, int in_len,
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
+			if (out_pos >= out_end)
+			{
+				/* We are losing some data. */
+				state->step = step_c;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 			curr_byte |= (fragment & 0x03c) >> 2;
 			*out_pos++ = curr_byte;
 			curr_byte = (fragment & 0x003) << 6;
-			if (out_pos < out_end)
-				*out_pos = curr_byte;
 	case step_d:
 			do {
-				if (in_pos == in_end || out_pos >= out_end)
+				if (in_pos >= in_end)
 				{
 					state->step = step_d;
 					state->result = curr_byte;
@@ -307,6 +317,13 @@ base64_decode_block(const char *in_base64, int in_len,
 				}
 				fragment = base64_decode_value(*in_pos++);
 			} while (fragment < 0);
+			if (out_pos >= out_end)
+			{
+				/* We are losing some data. */
+				state->step = step_d;
+				state->result = curr_byte;
+				return out_pos - out_bin;
+			}
 			curr_byte |= (fragment & 0x03f);
 			*out_pos++ = curr_byte;
 		}
-- 
2.25.1