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/*
* upb - a minimalist implementation of protocol buffers.
*
* Copyright (c) 2011 Google Inc. See LICENSE for details.
* Author: Josh Haberman <jhaberman@gmail.com>
*/
#include "upb/pb/varint.h"
// A basic branch-based decoder, uses 32-bit values to get good performance
// on 32-bit architectures (but performs well on 64-bits also).
// This scheme comes from the original Google Protobuf implementation (proto2).
upb_decoderet upb_vdecode_max8_branch32(upb_decoderet r) {
upb_decoderet err = {NULL, 0};
const char *p = r.p;
uint32_t low = (uint32_t)r.val;
uint32_t high = 0;
uint32_t b;
b = *(p++); low |= (b & 0x7fU) << 14; if (!(b & 0x80)) goto done;
b = *(p++); low |= (b & 0x7fU) << 21; if (!(b & 0x80)) goto done;
b = *(p++); low |= (b & 0x7fU) << 28;
high = (b & 0x7fU) >> 4; if (!(b & 0x80)) goto done;
b = *(p++); high |= (b & 0x7fU) << 3; if (!(b & 0x80)) goto done;
b = *(p++); high |= (b & 0x7fU) << 10; if (!(b & 0x80)) goto done;
b = *(p++); high |= (b & 0x7fU) << 17; if (!(b & 0x80)) goto done;
b = *(p++); high |= (b & 0x7fU) << 24; if (!(b & 0x80)) goto done;
b = *(p++); high |= (b & 0x7fU) << 31; if (!(b & 0x80)) goto done;
return err;
done:
r.val = ((uint64_t)high << 32) | low;
r.p = p;
return r;
}
// Like the previous, but uses 64-bit values.
upb_decoderet upb_vdecode_max8_branch64(upb_decoderet r) {
const char *p = r.p;
uint64_t val = r.val;
uint64_t b;
upb_decoderet err = {NULL, 0};
b = *(p++); val |= (b & 0x7fU) << 14; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 21; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 28; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 35; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 42; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 49; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 56; if (!(b & 0x80)) goto done;
b = *(p++); val |= (b & 0x7fU) << 63; if (!(b & 0x80)) goto done;
return err;
done:
r.val = val;
r.p = p;
return r;
}
// Given an encoded varint v, returns an integer with a single bit set that
// indicates the end of the varint. Subtracting one from this value will
// yield a mask that leaves only bits that are part of the varint. Returns
// 0 if the varint is unterminated.
static uint64_t upb_get_vstopbit(uint64_t v) {
uint64_t cbits = v | 0x7f7f7f7f7f7f7f7fULL;
return ~cbits & (cbits+1);
}
// A branchless decoder. Credit to Pascal Massimino for the bit-twiddling.
upb_decoderet upb_vdecode_max8_massimino(upb_decoderet r) {
uint64_t b;
memcpy(&b, r.p, sizeof(b));
uint64_t stop_bit = upb_get_vstopbit(b);
b = (b & 0x7f7f7f7f7f7f7f7fULL) & (stop_bit - 1);
b += b & 0x007f007f007f007fULL;
b += 3 * (b & 0x0000ffff0000ffffULL);
b += 15 * (b & 0x00000000ffffffffULL);
if (stop_bit == 0) {
// Error: unterminated varint.
upb_decoderet err_r = {(void*)0, 0};
return err_r;
}
upb_decoderet my_r = {r.p + ((__builtin_ctzll(stop_bit) + 1) / 8),
r.val | (b << 7)};
return my_r;
}
// A branchless decoder. Credit to Daniel Wright for the bit-twiddling.
upb_decoderet upb_vdecode_max8_wright(upb_decoderet r) {
uint64_t b;
memcpy(&b, r.p, sizeof(b));
uint64_t stop_bit = upb_get_vstopbit(b);
b &= (stop_bit - 1);
b = ((b & 0x7f007f007f007f00ULL) >> 1) | (b & 0x007f007f007f007fULL);
b = ((b & 0xffff0000ffff0000ULL) >> 2) | (b & 0x0000ffff0000ffffULL);
b = ((b & 0xffffffff00000000ULL) >> 4) | (b & 0x00000000ffffffffULL);
if (stop_bit == 0) {
// Error: unterminated varint.
upb_decoderet err_r = {(void*)0, 0};
return err_r;
}
upb_decoderet my_r = {r.p + ((__builtin_ctzll(stop_bit) + 1) / 8),
r.val | (b << 14)};
return my_r;
}
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