Split varint decoders into separate .h file.

This makes it easier to benchmark and test the
multiple possible implementations of varint decoding.

src/upb_varint_decoder.h

@@ -0,0 +1,120 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * A number of routines for varint decoding (we keep them all around to have
+ * multiple approaches available for benchmarking).  All of these functions
+ * require the buffer to have at least 10 bytes available; if we don't know
+ * for sure that there are 10 bytes, then there is only one viable option
+ * (branching on every byte).
+ *
+ * Copyright (c) 2011 Joshua Haberman.  See LICENSE for details.
+ */
+
+#ifndef UPB_VARINT_DECODER_H_
+#define UPB_VARINT_DECODER_H_
+
+#include "upb.h"
+#include <stdint.h>
+#include <string.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// All decoding functions return this struct by value.
+typedef struct {
+  const char *p;  // NULL if the varint was unterminated.
+  uint64_t val;
+} upb_decoderet;
+
+// A basic branch-based decoder, uses 32-bit values to get good performance
+// on 32-bit architectures (but performs well on 64-bits also).
+INLINE upb_decoderet upb_decode_varint_branch32(const char *p) {
+  upb_decoderet r = {NULL, 0};
+  uint32_t low, high = 0;
+  uint32_t b;
+  b = *(p++); low   = (b & 0x7f)      ; if(!(b & 0x80)) goto done;
+  b = *(p++); low  |= (b & 0x7f) <<  7; if(!(b & 0x80)) goto done;
+  b = *(p++); low  |= (b & 0x7f) << 14; if(!(b & 0x80)) goto done;
+  b = *(p++); low  |= (b & 0x7f) << 21; if(!(b & 0x80)) goto done;
+  b = *(p++); low  |= (b & 0x7f) << 28;
+              high  = (b & 0x7f) >>  4; if(!(b & 0x80)) goto done;
+  b = *(p++); high |= (b & 0x7f) <<  3; if(!(b & 0x80)) goto done;
+  b = *(p++); high |= (b & 0x7f) << 10; if(!(b & 0x80)) goto done;
+  b = *(p++); high |= (b & 0x7f) << 17; if(!(b & 0x80)) goto done;
+  b = *(p++); high |= (b & 0x7f) << 24; if(!(b & 0x80)) goto done;
+  b = *(p++); high |= (b & 0x7f) << 31; if(!(b & 0x80)) goto done;
+  return r;
+
+done:
+  r.val = ((uint64_t)high << 32) | low;
+  r.p = p;
+  return r;
+}
+
+// Like the previous, but uses 64-bit values.
+INLINE upb_decoderet upb_decode_varint_branch64(const char *p) {
+  uint64_t val;
+  uint64_t b;
+  upb_decoderet r = {(void*)0, 0};
+  b = *(p++); val  = (b & 0x7f)      ; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) <<  7; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 14; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 21; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 28; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 35; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 42; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 49; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 56; if(!(b & 0x80)) goto done;
+  b = *(p++); val |= (b & 0x7f) << 63; if(!(b & 0x80)) goto done;
+  return r;
+
+done:
+  r.val = val;
+  r.p = p;
+  return r;
+}
+
+#ifdef __SSE__
+
+#include <xmmintrin.h>
+
+// Avoids branches (this can very likely be improved).  Requires SSE.
+INLINE upb_decoderet upb_decode_varint_nobranch(const char *p) {
+  upb_decoderet r = {(void*)0, 0};
+  __m128i val128 = _mm_loadu_si128((void*)p);
+  unsigned int continuation_bits = _mm_movemask_epi8(val128);
+  unsigned int bsr_val = ~continuation_bits;
+  int varint_length = __builtin_ffs(bsr_val);
+  if (varint_length > 10) return r;
+
+  uint16_t twob;
+  memcpy(&twob, p, 2);
+  twob &= 0x7f7f;
+  twob = ((twob & 0xff00) >> 1) | (twob & 0xff);
+
+  uint64_t eightb;
+  memcpy(&eightb, p + 2, 8);
+  eightb &= 0x7f7f7f7f7f7f7f7f;
+  eightb = ((eightb & 0xff00ff00ff00ff00) >> 1) | (eightb & 0x00ff00ff00ff00ff);
+  eightb = ((eightb & 0xffff0000ffff0000) >> 2) | (eightb & 0x0000ffff0000ffff);
+  eightb = ((eightb & 0xffffffff00000000) >> 4) | (eightb & 0x00000000ffffffff);
+
+  uint64_t all_bits = twob | (eightb << 14);
+  int varint_bits = varint_length * 7;
+  uint64_t mask = varint_bits == 70 ? (uint64_t)-1 : (1ULL << (varint_bits)) - 1;
+  r.val = all_bits & mask;
+  r.p = p + varint_length;
+  return r;
+}
+
+#endif
+
+// For now, always use the branch32 decoder.
+#define upb_decode_varint_fast upb_decode_varint_branch32
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* UPB_VARINT_DECODER_H_ */

tests/test_varint.c

@@ -0,0 +1,216 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2011 Joshua Haberman.  See LICENSE for details.
+ */
+
+#include "upb_varint_decoder.h"
+#include "upb_test.h"
+
+static void test_varint_decoder(upb_decoderet (*decoder)(const char*)) {
+#define TEST(bytes, expected_val) {\
+    const char buf[] = bytes "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" ; \
+    upb_decoderet r = decoder(buf); \
+    ASSERT(r.val == expected_val); \
+    ASSERT(r.p == buf + sizeof(buf) - 16);  /* - 1 for NULL */ \
+  }
+
+  TEST("\x00",                                                      0ULL);
+  TEST("\x01",                                                      1ULL);
+  TEST("\x81\x14",                                              0xa01ULL);
+  TEST("\x81\x03",                                              0x181ULL);
+  TEST("\x81\x83\x07",                                        0x1c181ULL);
+  TEST("\x81\x83\x87\x0f",                                  0x1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x1f",                            0x1f1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x9f\x3f",                      0x1f9f1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x9f\xbf\x7f",                0x1fdf9f1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x9f\xbf\xff\x01",            0x3fdf9f1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x9f\xbf\xff\x81\x03",      0x303fdf9f1e1c181ULL);
+  TEST("\x81\x83\x87\x8f\x9f\xbf\xff\x81\x83\x07", 0x8303fdf9f1e1c181ULL);
+#undef TEST
+
+  char twelvebyte[16] = {0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x01, 0x01};
+  const char *twelvebyte_buf = twelvebyte;
+  // A varint that terminates before hitting the end of the provided buffer,
+  // but in too many bytes (11 instead of 10).
+  upb_decoderet r = upb_decode_varint_fast(twelvebyte_buf);
+  ASSERT(r.p == NULL);
+}
+
+
+#define TEST_VARINT_DECODER(decoder) \
+  /* Create non-inline versions for convenient inspection of assembly language \
+   * output. */ \
+  upb_decoderet _upb_decode_varint_ ## decoder(const char *p) { \
+    return upb_decode_varint_ ## decoder(p); \
+  } \
+  void test_ ## decoder() { \
+    test_varint_decoder(&_upb_decode_varint_ ## decoder); \
+  } \
+
+TEST_VARINT_DECODER(branch32);
+TEST_VARINT_DECODER(branch64);
+#ifdef __SSE__
+TEST_VARINT_DECODER(nobranch);
+#endif
+
+int main() {
+  test_branch32();
+  test_branch64();
+#ifdef __SSE__
+  test_nobranch();
+#endif
+}
+
+#if 0
+static void test_get_v_uint32_t()
+{
+#define TEST(name, bytes, val) {\
+    upb_status status = UPB_STATUS_INIT; \
+    const uint8_t name[] = bytes; \
+    const uint8_t *name ## _buf = name; \
+    uint32_t name ## _val = 0; \
+    name ## _buf = upb_get_v_uint32_t(name, name + sizeof(name), &name ## _val, &status); \
+    ASSERT(upb_ok(&status)); \
+    ASSERT(name ## _val == val); \
+    ASSERT(name ## _buf == name + sizeof(name) - 1);  /* - 1 for NULL */ \
+    /* Test NEED_MORE_DATA. */ \
+    if(sizeof(name) > 2) { \
+      name ## _buf = upb_get_v_uint32_t(name, name + sizeof(name) - 2, &name ## _val, &status); \
+      ASSERT(status.code == UPB_STATUS_NEED_MORE_DATA); \
+    } \
+  }
+
+  TEST(zero,   "\x00",                                              0UL);
+  TEST(one,    "\x01",                                              1UL);
+  TEST(twob,   "\x81\x03",                                      0x181UL);
+  TEST(threeb, "\x81\x83\x07",                                0x1c181UL);
+  TEST(fourb,  "\x81\x83\x87\x0f",                          0x1e1c181UL);
+  /* get_v_uint32_t truncates, so all the rest return the same thing. */
+  TEST(fiveb,  "\x81\x83\x87\x8f\x1f",                     0xf1e1c181UL);
+  TEST(sixb,   "\x81\x83\x87\x8f\x9f\x3f",                 0xf1e1c181UL);
+  TEST(sevenb, "\x81\x83\x87\x8f\x9f\xbf\x7f",             0xf1e1c181UL);
+  TEST(eightb, "\x81\x83\x87\x8f\x9f\xbf\xff\x01",         0xf1e1c181UL);
+  TEST(nineb,  "\x81\x83\x87\x8f\x9f\xbf\xff\x81\x03",     0xf1e1c181UL);
+  TEST(tenb,   "\x81\x83\x87\x8f\x9f\xbf\xff\x81\x83\x07", 0xf1e1c181UL);
+#undef TEST
+
+  uint8_t twelvebyte[] = {0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x01, 0x01};
+  uint32_t twelvebyte_val = 0;
+  upb_status status = UPB_STATUS_INIT;
+  /* A varint that terminates before hitting the end of the provided buffer,
+   * but in too many bytes (11 instead of 10). */
+  upb_get_v_uint32_t(twelvebyte, twelvebyte + 12, &twelvebyte_val, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT);
+
+  /* A varint that terminates simultaneously with the end of the provided
+   * buffer, but in too many bytes (11 instead of 10). */
+  upb_reset(&status);
+  upb_get_v_uint32_t(twelvebyte, twelvebyte + 11, &twelvebyte_val, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT);
+
+  /* A varint whose buffer ends on exactly the byte where the varint must
+   * terminate, but the final byte does not terminate.  The absolutely most
+   * correct return code here is UPB_ERROR_UNTERMINATED_VARINT, because we know
+   * by this point that the varint does not properly terminate.  But we also
+   * allow a return value of UPB_STATUS_NEED_MORE_DATA here, because it does not
+   * compromise overall correctness -- clients who supply more data later will
+   * then receive a UPB_ERROR_UNTERMINATED_VARINT error; clients who have no
+   * more data to supply will (rightly) conclude that their protobuf is corrupt.
+   */
+  upb_reset(&status);
+  upb_get_v_uint32_t(twelvebyte, twelvebyte + 10, &twelvebyte_val, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT ||
+         status.code == UPB_STATUS_NEED_MORE_DATA);
+
+  upb_reset(&status);
+  upb_get_v_uint32_t(twelvebyte, twelvebyte + 9, &twelvebyte_val, &status);
+  ASSERT(status.code == UPB_STATUS_NEED_MORE_DATA);
+}
+
+static void test_skip_v_uint64_t()
+{
+#define TEST(name, bytes) {\
+    upb_status status = UPB_STATUS_INIT; \
+    const uint8_t name[] = bytes; \
+    const uint8_t *name ## _buf = name; \
+    name ## _buf = upb_skip_v_uint64_t(name ## _buf, name + sizeof(name), &status); \
+    ASSERT(upb_ok(&status)); \
+    ASSERT(name ## _buf == name + sizeof(name) - 1);  /* - 1 for NULL */ \
+    /* Test NEED_MORE_DATA. */ \
+    if(sizeof(name) > 2) { \
+      name ## _buf = upb_skip_v_uint64_t(name, name + sizeof(name) - 2, &status); \
+      ASSERT(status.code == UPB_STATUS_NEED_MORE_DATA); \
+    } \
+  }
+
+  TEST(zero,   "\x00");
+  TEST(one,    "\x01");
+  TEST(twob,   "\x81\x03");
+  TEST(threeb, "\x81\x83\x07");
+  TEST(fourb,  "\x81\x83\x87\x0f");
+  TEST(fiveb,  "\x81\x83\x87\x8f\x1f");
+  TEST(sixb,   "\x81\x83\x87\x8f\x9f\x3f");
+  TEST(sevenb, "\x81\x83\x87\x8f\x9f\xbf\x7f");
+  TEST(eightb, "\x81\x83\x87\x8f\x9f\xbf\xff\x01");
+  TEST(nineb,  "\x81\x83\x87\x8f\x9f\xbf\xff\x81\x03");
+  TEST(tenb,   "\x81\x83\x87\x8f\x9f\xbf\xff\x81\x83\x07");
+#undef TEST
+
+  uint8_t twelvebyte[] = {0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x80, 0x01, 0x01};
+  upb_status status = UPB_STATUS_INIT;
+  /* A varint that terminates before hitting the end of the provided buffer,
+   * but in too many bytes (11 instead of 10). */
+  upb_skip_v_uint64_t(twelvebyte, twelvebyte + 12, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT);
+
+  /* A varint that terminates simultaneously with the end of the provided
+   * buffer, but in too many bytes (11 instead of 10). */
+  upb_reset(&status);
+  upb_skip_v_uint64_t(twelvebyte, twelvebyte + 11, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT);
+
+  /* A varint whose buffer ends on exactly the byte where the varint must
+   * terminate, but the final byte does not terminate.  The absolutely most
+   * correct return code here is UPB_ERROR_UNTERMINATED_VARINT, because we know
+   * by this point that the varint does not properly terminate.  But we also
+   * allow a return value of UPB_STATUS_NEED_MORE_DATA here, because it does not
+   * compromise overall correctness -- clients who supply more data later will
+   * then receive a UPB_ERROR_UNTERMINATED_VARINT error; clients who have no
+   * more data to supply will (rightly) conclude that their protobuf is corrupt.
+   */
+  upb_reset(&status);
+  upb_skip_v_uint64_t(twelvebyte, twelvebyte + 10, &status);
+  ASSERT(status.code == UPB_ERROR_UNTERMINATED_VARINT ||
+         status.code == UPB_STATUS_NEED_MORE_DATA);
+
+  upb_reset(&status);
+  upb_skip_v_uint64_t(twelvebyte, twelvebyte + 9, &status);
+  ASSERT(status.code == UPB_STATUS_NEED_MORE_DATA);
+}
+
+static void test_get_f_uint32_t()
+{
+#define TEST(name, bytes, val) {\
+    upb_status status = UPB_STATUS_INIT; \
+    const uint8_t name[] = bytes; \
+    const uint8_t *name ## _buf = name; \
+    uint32_t name ## _val = 0; \
+    name ## _buf = upb_get_f_uint32_t(name ## _buf, name + sizeof(name), &name ## _val, &status); \
+    ASSERT(upb_ok(&status)); \
+    ASSERT(name ## _val == val); \
+    ASSERT(name ## _buf == name + sizeof(name) - 1);  /* - 1 for NULL */ \
+  }
+
+  TEST(zero,  "\x00\x00\x00\x00",                                0x0UL);
+  TEST(one,   "\x01\x00\x00\x00",                                0x1UL);
+
+  uint8_t threeb[] = {0x00, 0x00, 0x00};
+  uint32_t threeb_val;
+  upb_status status = UPB_STATUS_INIT;
+  upb_get_f_uint32_t(threeb, threeb + sizeof(threeb), &threeb_val, &status);
+  ASSERT(status.code == UPB_STATUS_NEED_MORE_DATA);
+
+#undef TEST
+}
+#endif

tests/upb_test.h

@@ -0,0 +1,27 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2011 Joshua Haberman.  See LICENSE for details.
+ */
+
+#ifndef UPB_TEST_H_
+#define UPB_TEST_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int num_assertions = 0;
+#define ASSERT(expr) do { \
+  ++num_assertions; \
+  if (!(expr)) { \
+    fprintf(stderr, "Assertion failed: %s:%d\n", __FILE__, __LINE__); \
+    abort(); \
+  } \
+} while(0)
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* UPB_DECODER_H_ */