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Improve field list calculation code (#221)
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More general support for fixed size constants in calculation (arbitrary
width), by re-using deparser code. Added a unit test for non-aligned
constants in calculations. Code cleanup.
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@antoninbas
antoninbas authored Oct 19, 2016
1 parent c602190 commit f53451a
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Showing 6 changed files with 186 additions and 139 deletions.
99 changes: 12 additions & 87 deletions include/bm/bm_sim/calculations.h
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Original file line number Diff line number Diff line change
Expand Up @@ -226,7 +226,16 @@ class RawCalculation
};


struct BufBuilder {
class BufBuilder {
public:
void push_back_field(header_id_t header, int field_offset);
void push_back_constant(const ByteContainer &v, size_t nbits);
void push_back_header(header_id_t header);
void append_payload();

void operator()(const Packet &pkt, ByteContainer *buf) const;

private:
struct field_t {
header_id_t header;
int field_offset;
Expand All @@ -241,94 +250,10 @@ struct BufBuilder {
header_id_t header;
};

struct Deparse; // defined in calculations.cpp

std::vector<boost::variant<field_t, constant_t, header_t> > entries{};
bool with_payload{false};

void push_back_field(header_id_t header, int field_offset) {
field_t f = {header, field_offset};
entries.emplace_back(f);
}

void push_back_constant(const ByteContainer &v, size_t nbits) {
// TODO(antonin): general case
assert(nbits % 8 == 0);
constant_t c = {v, nbits};
entries.emplace_back(c);
}

void push_back_header(header_id_t header) {
header_t h = {header};
entries.emplace_back(h);
}

void append_payload() {
with_payload = true;
}

struct Deparse : public boost::static_visitor<> {
Deparse(const PHV &phv, ByteContainer *buf)
: phv(phv), buf(buf) { }

char *extend(int more_bits) {
int nbits_ = nbits + more_bits;
buf->resize((nbits_ + 7) / 8, '\x00');
char *ptr = buf->data() + (nbits / 8);
nbits = nbits_;
// needed ?
// if (new_bytes > 0) buf->back() = '\x00';
return ptr;
}

int get_offset() const {
return nbits % 8;
}

void operator()(const field_t &f) {
const Header &header = phv.get_header(f.header);
if (!header.is_valid()) return;
const Field &field = header.get_field(f.field_offset);
// taken from headers.cpp::deparse
const int offset = get_offset();
field.deparse(extend(field.get_nbits()), offset);
}

void operator()(const constant_t &c) {
assert(get_offset() == 0);
std::copy(c.v.begin(), c.v.end(), extend(c.nbits));
}

void operator()(const header_t &h) {
assert(get_offset() == 0);
const Header &header = phv.get_header(h.header);
if (header.is_valid()) {
header.deparse(extend(header.get_nbytes_packet() * 8));
}
}

Deparse(const Deparse &other) = delete;
Deparse &operator=(const Deparse &other) = delete;

Deparse(Deparse &&other) = delete;
Deparse &operator=(Deparse &&other) = delete;

const PHV &phv;
ByteContainer *buf;
int nbits{0};
};

void operator()(const Packet &pkt, ByteContainer *buf) const {
buf->clear();
const PHV *phv = pkt.get_phv();
Deparse visitor(*phv, buf);
std::for_each(entries.begin(), entries.end(),
boost::apply_visitor(visitor));
if (with_payload) {
size_t curr = buf->size();
size_t psize = pkt.get_data_size();
buf->resize(curr + psize);
std::copy(pkt.data(), pkt.data() + psize, buf->begin() + curr);
}
}
};


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89 changes: 89 additions & 0 deletions src/bm_sim/calculations.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -29,9 +29,98 @@

#include "xxhash.h"
#include "crc_tables.h"
#include "extract.h"

namespace bm {

void
BufBuilder::push_back_field(header_id_t header, int field_offset) {
field_t f = {header, field_offset};
entries.emplace_back(f);
}

void
BufBuilder::push_back_constant(const ByteContainer &v, size_t nbits) {
constant_t c = {v, nbits};
entries.emplace_back(c);
}

void
BufBuilder::push_back_header(header_id_t header) {
header_t h = {header};
entries.emplace_back(h);
}

void
BufBuilder::append_payload() {
with_payload = true;
}

struct BufBuilder::Deparse : public boost::static_visitor<> {
Deparse(const PHV &phv, ByteContainer *buf, int init_offset = 0)
: phv(phv), buf(buf), nbits(init_offset) { }

char *extend(int more_bits) {
int nbits_ = nbits + more_bits;
buf->resize((nbits_ + 7) / 8, '\x00');
char *ptr = buf->data() + (nbits / 8);
nbits = nbits_;
return ptr;
}

int get_offset() const {
return nbits % 8;
}

void operator()(const field_t &f) {
const Header &header = phv.get_header(f.header);
if (!header.is_valid()) return;
const Field &field = header.get_field(f.field_offset);
// get_offset needs to be called before extend!
const auto offset = get_offset();
field.deparse(extend(field.get_nbits()), offset);
}

void operator()(const constant_t &c) {
// get_offset needs to be called before extend!
const auto offset = get_offset();
extract::generic_deparse(&c.v[0], c.nbits, extend(c.nbits), offset);
}

void operator()(const header_t &h) {
assert(get_offset() == 0);
const Header &header = phv.get_header(h.header);
if (header.is_valid()) {
header.deparse(extend(header.get_nbytes_packet() * 8));
}
}

Deparse(const Deparse &other) = delete;
Deparse &operator=(const Deparse &other) = delete;

Deparse(Deparse &&other) = delete;
Deparse &operator=(Deparse &&other) = delete;

const PHV &phv;
ByteContainer *buf;
int nbits{0};
};

void
BufBuilder::operator()(const Packet &pkt, ByteContainer *buf) const {
buf->clear();
const PHV *phv = pkt.get_phv();
Deparse visitor(*phv, buf);
std::for_each(entries.begin(), entries.end(),
boost::apply_visitor(visitor));
if (with_payload) {
size_t curr = buf->size();
size_t psize = pkt.get_data_size();
buf->resize(curr + psize);
std::copy(pkt.data(), pkt.data() + psize, buf->begin() + curr);
}
}

namespace hash {

uint64_t xxh64(const char *buffer, size_t s) {
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59 changes: 56 additions & 3 deletions src/bm_sim/extract.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,12 +21,14 @@
#ifndef BM_SIM_EXTRACT_H_
#define BM_SIM_EXTRACT_H_

#include <algorithm> // for std::fill, std::copy

namespace bm {

namespace extract {

static void generic_extract(const char *data, int bit_offset,
int bitwidth, char *dst) {
static inline void generic_extract(const char *data, int bit_offset,
int bitwidth, char *dst) {
int nbytes = (bitwidth + 7) / 8;

if (bit_offset == 0 && bitwidth % 8 == 0) {
Expand All @@ -39,7 +41,7 @@ static void generic_extract(const char *data, int bit_offset,

// necessary to ensure correct behavior when shifting right (no sign
// extension)
unsigned char *udata = (unsigned char *) data;
auto udata = reinterpret_cast<const unsigned char *>(data);

int offset = bit_offset - dst_offset;
if (offset == 0) {
Expand All @@ -64,6 +66,57 @@ static void generic_extract(const char *data, int bit_offset,
}
}

static inline void generic_deparse(const char *data, int bitwidth,
char *dst, int hdr_offset) {
int nbytes = (bitwidth + 7) / 8;

if (hdr_offset == 0 && bitwidth % 8 == 0) {
memcpy(dst, data, nbytes);
return;
}

int field_offset = (nbytes << 3) - bitwidth;
int hdr_bytes = (hdr_offset + bitwidth + 7) / 8;

int i;

// necessary to ensure correct behavior when shifting right (no sign
// extension)
auto udata = reinterpret_cast<const unsigned char *>(data);

// zero out bits we are going to write in dst[0]
dst[0] &= (~(0xFF >> hdr_offset));

int offset = field_offset - hdr_offset;
if (offset == 0) {
std::copy(data + 1, data + hdr_bytes, dst + 1);
dst[0] |= udata[0];
} else if (offset > 0) { // shift left
// don't know if this is very efficient, we memset the remaining bytes to 0
// so we can use |= and preserve what was originally in dst[0]
std::fill(&dst[1], &dst[hdr_bytes], 0);
for (i = 0; i < hdr_bytes - 1; i++) {
dst[i] |= (udata[i] << offset) | (udata[i + 1] >> (8 - offset));
}
dst[i] |= udata[i] << offset;
} else { // shift right
offset = -offset;
dst[0] |= (udata[0] >> offset);
if (nbytes == 1) {
// dst[1] is always valid, otherwise we would not need to shift the field
// to the right
dst[1] = udata[0] << (8 - offset);
return;
}
for (i = 1; i < hdr_bytes - 1; i++) {
dst[i] = (udata[i - 1] << (8 - offset)) | (udata[i] >> offset);
}
int tail_offset = (hdr_bytes << 3) - (hdr_offset + bitwidth);
dst[i] &= ((1 << tail_offset) - 1);
dst[i] |= (udata[i - 1] << (8 - offset));
}
}

} // namespace extract

} // namespace bm
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49 changes: 1 addition & 48 deletions src/bm_sim/fields.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20,8 +20,6 @@

#include <bm/bm_sim/fields.h>

#include <algorithm>

#include "extract.h"

namespace bm {
Expand All @@ -43,52 +41,7 @@ int Field::extract_VL(const char *data, int hdr_offset, int computed_nbits) {
}

int Field::deparse(char *data, int hdr_offset) const {
if (hdr_offset == 0 && nbits % 8 == 0) {
std::copy(bytes.begin(), bytes.end(), data);
return nbits;
}

int field_offset = (nbytes << 3) - nbits;
int hdr_bytes = (hdr_offset + nbits + 7) / 8;

int i;

// necessary to ensure correct behavior when shifting right (no sign
// extension)
unsigned char *ubytes = (unsigned char *) bytes.data();

// zero out bits we are going to write in data[0]
data[0] &= (~(0xFF >> hdr_offset));

int offset = field_offset - hdr_offset;
if (offset == 0) {
std::copy(bytes.begin() + 1, bytes.begin() + hdr_bytes, data + 1);
data[0] |= ubytes[0];
} else if (offset > 0) { // shift left
// don't know if this is very efficient, we memset the remaining bytes to 0
// so we can use |= and preserve what was originally in data[0]
std::fill(&data[1], &data[hdr_bytes], 0);
for (i = 0; i < hdr_bytes - 1; i++) {
data[i] |= (ubytes[i] << offset) | (ubytes[i + 1] >> (8 - offset));
}
data[i] |= ubytes[i] << offset;
} else { // shift right
offset = -offset;
data[0] |= (ubytes[0] >> offset);
if (nbytes == 1) {
// data[1] is always valid, otherwise we would not need to shift the field
// to the right
data[1] = ubytes[0] << (8 - offset);
return nbits;
}
for (i = 1; i < hdr_bytes - 1; i++) {
data[i] = (ubytes[i - 1] << (8 - offset)) | (ubytes[i] >> offset);
}
int tail_offset = (hdr_bytes << 3) - (hdr_offset + nbits);
data[i] &= ((1 << tail_offset) - 1);
data[i] |= (ubytes[i - 1] << (8 - offset));
}

extract::generic_deparse(&bytes[0], nbits, data, hdr_offset);
return nbits;
}

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27 changes: 27 additions & 0 deletions tests/test_calculations.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,33 @@ TEST_F(CalculationTest, WithConstant) {
ASSERT_EQ(expected, actual);
}

TEST_F(CalculationTest, WithConstantNonAligned) {
BufBuilder builder;

// 0x9fd = 1001 1111 1101
ByteContainer constant("0x9fd");

builder.push_back_constant(ByteContainer("0x00"), 4);
builder.push_back_field(testHeader1, 0); // f16
builder.push_back_constant(constant, 12);

Calculation calc(builder, "identity");

unsigned char pkt_buf[2 * header_size];

for (size_t i = 0; i < sizeof(pkt_buf); i++) {
pkt_buf[i] = 0xff;
}

Packet pkt = get_pkt((const char *) pkt_buf, sizeof(pkt_buf));
parser.parse(&pkt);

auto expected = static_cast<uint64_t>(0x0ffff9fd);
auto actual = calc.output(pkt);

ASSERT_EQ(expected, actual);
}

TEST_F(CalculationTest, WithPayload) {
BufBuilder builder;

Expand Down
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