diff options
Diffstat (limited to 'upb/pb/varint.int.h')
| -rw-r--r-- | upb/pb/varint.int.h | 86 |
1 files changed, 51 insertions, 35 deletions
diff --git a/upb/pb/varint.int.h b/upb/pb/varint.int.h index 8498acd..a394a75 100644 --- a/upb/pb/varint.int.h +++ b/upb/pb/varint.int.h @@ -20,25 +20,25 @@ extern "C" { #endif -// A list of types as they are encoded on-the-wire. +/* A list of types as they are encoded on-the-wire. */ typedef enum { UPB_WIRE_TYPE_VARINT = 0, UPB_WIRE_TYPE_64BIT = 1, UPB_WIRE_TYPE_DELIMITED = 2, UPB_WIRE_TYPE_START_GROUP = 3, UPB_WIRE_TYPE_END_GROUP = 4, - UPB_WIRE_TYPE_32BIT = 5, + UPB_WIRE_TYPE_32BIT = 5 } upb_wiretype_t; #define UPB_MAX_WIRE_TYPE 5 -// The maximum number of bytes that it takes to encode a 64-bit varint. -// Note that with a better encoding this could be 9 (TODO: write up a -// wiki document about this). +/* The maximum number of bytes that it takes to encode a 64-bit varint. + * Note that with a better encoding this could be 9 (TODO: write up a + * wiki document about this). */ #define UPB_PB_VARINT_MAX_LEN 10 -// Array of the "native" (ie. non-packed-repeated) wire type for the given a -// descriptor type (upb_descriptortype_t). +/* Array of the "native" (ie. non-packed-repeated) wire type for the given a + * descriptor type (upb_descriptortype_t). */ extern const uint8_t upb_pb_native_wire_types[]; /* Zig-zag encoding/decoding **************************************************/ @@ -54,44 +54,59 @@ UPB_INLINE uint64_t upb_zzenc_64(int64_t n) { return (n << 1) ^ (n >> 63); } /* Decoding *******************************************************************/ -// All decoding functions return this struct by value. +/* All decoding functions return this struct by value. */ typedef struct { - const char *p; // NULL if the varint was unterminated. + const char *p; /* NULL if the varint was unterminated. */ uint64_t val; } upb_decoderet; -// Four functions for decoding a varint of at most eight bytes. They are all -// functionally identical, but are implemented in different ways and likely have -// different performance profiles. We keep them around for performance testing. -// -// Note that these functions may not read byte-by-byte, so they must not be used -// unless there are at least eight bytes left in the buffer! +UPB_INLINE upb_decoderet upb_decoderet_make(const char *p, uint64_t val) { + upb_decoderet ret; + ret.p = p; + ret.val = val; + return ret; +} + +/* Four functions for decoding a varint of at most eight bytes. They are all + * functionally identical, but are implemented in different ways and likely have + * different performance profiles. We keep them around for performance testing. + * + * Note that these functions may not read byte-by-byte, so they must not be used + * unless there are at least eight bytes left in the buffer! */ upb_decoderet upb_vdecode_max8_branch32(upb_decoderet r); upb_decoderet upb_vdecode_max8_branch64(upb_decoderet r); upb_decoderet upb_vdecode_max8_wright(upb_decoderet r); upb_decoderet upb_vdecode_max8_massimino(upb_decoderet r); -// Template for a function that checks the first two bytes with branching -// and dispatches 2-10 bytes with a separate function. Note that this may read -// up to 10 bytes, so it must not be used unless there are at least ten bytes -// left in the buffer! +/* Template for a function that checks the first two bytes with branching + * and dispatches 2-10 bytes with a separate function. Note that this may read + * up to 10 bytes, so it must not be used unless there are at least ten bytes + * left in the buffer! */ #define UPB_VARINT_DECODER_CHECK2(name, decode_max8_function) \ UPB_INLINE upb_decoderet upb_vdecode_check2_ ## name(const char *_p) { \ uint8_t *p = (uint8_t*)_p; \ - if ((*p & 0x80) == 0) { upb_decoderet r = {_p + 1, *p & 0x7fU}; return r; } \ - upb_decoderet r = {_p + 2, (*p & 0x7fU) | ((*(p + 1) & 0x7fU) << 7)}; \ - if ((*(p + 1) & 0x80) == 0) return r; \ + upb_decoderet r; \ + if ((*p & 0x80) == 0) { \ + /* Common case: one-byte varint. */ \ + return upb_decoderet_make(_p + 1, *p & 0x7fU); \ + } \ + r = upb_decoderet_make(_p + 2, (*p & 0x7fU) | ((*(p + 1) & 0x7fU) << 7)); \ + if ((*(p + 1) & 0x80) == 0) { \ + /* Two-byte varint. */ \ + return r; \ + } \ + /* Longer varint, fallback to out-of-line function. */ \ return decode_max8_function(r); \ } -UPB_VARINT_DECODER_CHECK2(branch32, upb_vdecode_max8_branch32); -UPB_VARINT_DECODER_CHECK2(branch64, upb_vdecode_max8_branch64); -UPB_VARINT_DECODER_CHECK2(wright, upb_vdecode_max8_wright); -UPB_VARINT_DECODER_CHECK2(massimino, upb_vdecode_max8_massimino); +UPB_VARINT_DECODER_CHECK2(branch32, upb_vdecode_max8_branch32) +UPB_VARINT_DECODER_CHECK2(branch64, upb_vdecode_max8_branch64) +UPB_VARINT_DECODER_CHECK2(wright, upb_vdecode_max8_wright) +UPB_VARINT_DECODER_CHECK2(massimino, upb_vdecode_max8_massimino) #undef UPB_VARINT_DECODER_CHECK2 -// Our canonical functions for decoding varints, based on the currently -// favored best-performing implementations. +/* Our canonical functions for decoding varints, based on the currently + * favored best-performing implementations. */ UPB_INLINE upb_decoderet upb_vdecode_fast(const char *p) { if (sizeof(long) == 8) return upb_vdecode_check2_branch64(p); @@ -108,7 +123,7 @@ UPB_INLINE upb_decoderet upb_vdecode_max8_fast(upb_decoderet r) { UPB_INLINE int upb_value_size(uint64_t val) { #ifdef __GNUC__ - int high_bit = 63 - __builtin_clzll(val); // 0-based, undef if val == 0. + int high_bit = 63 - __builtin_clzll(val); /* 0-based, undef if val == 0. */ #else int high_bit = 0; uint64_t tmp = val; @@ -117,13 +132,14 @@ UPB_INLINE int upb_value_size(uint64_t val) { return val == 0 ? 1 : high_bit / 8 + 1; } -// Encodes a 64-bit varint into buf (which must be >=UPB_PB_VARINT_MAX_LEN -// bytes long), returning how many bytes were used. -// -// TODO: benchmark and optimize if necessary. +/* Encodes a 64-bit varint into buf (which must be >=UPB_PB_VARINT_MAX_LEN + * bytes long), returning how many bytes were used. + * + * TODO: benchmark and optimize if necessary. */ UPB_INLINE size_t upb_vencode64(uint64_t val, char *buf) { + size_t i; if (val == 0) { buf[0] = 0; return 1; } - size_t i = 0; + i = 0; while (val) { uint8_t byte = val & 0x7fU; val >>= 7; @@ -138,7 +154,7 @@ UPB_INLINE size_t upb_varint_size(uint64_t val) { return upb_vencode64(val, buf); } -// Encodes a 32-bit varint, *not* sign-extended. +/* Encodes a 32-bit varint, *not* sign-extended. */ UPB_INLINE uint64_t upb_vencode32(uint32_t val) { char buf[UPB_PB_VARINT_MAX_LEN]; size_t bytes = upb_vencode64(val, buf); |