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dgb(share): rewire weight-decay arithmetic onto coin/share_weight_decay.hpp SSOT (#450 follow-on, value-invariant) #526

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dgb(share): rewire weight-decay arithmetic onto coin/share_weight_decay.hpp SSOT (#450 follow-on, value-invariant) #526

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27 changes: 12 additions & 15 deletions src/impl/dgb/share_tracker.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,7 @@ inline uint64_t mul128_shift(uint64_t a, uint64_t b, unsigned shift) {
#include "share_check.hpp"
#include "think_p1_walk_bounds.hpp" // SSOT: think_p1_walk_count / think_p1_in_pruning_zone
#include "coin/naughty_propagation.hpp" // SSOT: propagate_naughty_from_parent (data.py:543-549)
#include "coin/share_weight_decay.hpp" // SSOT: half_life/decay_per_share (#450, get_decayed_cumulative_weights)
#include <impl/dgb/coin/desired_version_tally.hpp> // SSOT: accumulate_version_weights / accumulate_version_counts (#429 follow-on)
#include "coin/pool_attempts_per_second.hpp" // SSOT: compute_pool_attempts_per_second (#407 follow-on)
#include "coin/tail_score_endpoints.hpp" // SSOT: score_* endpoint arithmetic (ShareTracker::score chain-walk, #411 follow-on)
Expand Down Expand Up @@ -159,9 +160,9 @@ struct PPLNSEntry {

class DensePPLNSWindow {
public:
static constexpr uint64_t DECAY_PRECISION = 40;
static constexpr uint64_t DECAY_SCALE = uint64_t(1) << DECAY_PRECISION;
static constexpr uint64_t LN2_MICRO = 693147;
// V36 decay constants sourced from coin/share_weight_decay.hpp SSOT (#450).
static constexpr uint64_t DECAY_PRECISION = dgb::coin::weight_decay::DECAY_PRECISION;
static constexpr uint64_t DECAY_SCALE = dgb::coin::weight_decay::DECAY_SCALE;

// Precomputed decay table: decay_table[d] = iterative decay factor at depth d.
// Computed once, reused for every PPLNS walk. Thread-safe after init.
Expand All @@ -172,8 +173,7 @@ class DensePPLNSWindow {
static void init_decay_table(uint32_t chain_len) {
if (s_table_initialized && s_decay_table.size() == chain_len)
return;
uint32_t half_life = std::max(chain_len / 4, uint32_t(1));
s_decay_per = DECAY_SCALE - (DECAY_SCALE * LN2_MICRO) / (uint64_t(1000000) * half_life);
s_decay_per = dgb::coin::weight_decay::decay_per_share(chain_len);
s_decay_table.resize(chain_len);
s_decay_table[0] = DECAY_SCALE;
for (uint32_t d = 1; d < chain_len; ++d)
Expand Down Expand Up @@ -1729,12 +1729,10 @@ class ShareTracker
&& m_decayed_cache_desired == desired_weight)
return m_decayed_cache_result;

static constexpr uint64_t DECAY_PRECISION = 40;
static constexpr uint64_t DECAY_SCALE = uint64_t(1) << DECAY_PRECISION;
static constexpr uint64_t LN2_MICRO = 693147;
static constexpr uint64_t DECAY_PRECISION = dgb::coin::weight_decay::DECAY_PRECISION;
static constexpr uint64_t DECAY_SCALE = dgb::coin::weight_decay::DECAY_SCALE;

uint32_t half_life = std::max(PoolConfig::chain_length() / 4, uint32_t(1));
uint64_t decay_per = DECAY_SCALE - (DECAY_SCALE * LN2_MICRO) / (uint64_t(1000000) * half_life);
uint64_t decay_per = dgb::coin::weight_decay::decay_per_share(PoolConfig::chain_length());

CumulativeWeights result;
int32_t share_count = 0;
Expand Down Expand Up @@ -1804,12 +1802,11 @@ class ShareTracker
return;
}

static constexpr uint64_t DECAY_PRECISION = 40;
static constexpr uint64_t DECAY_SCALE = uint64_t(1) << DECAY_PRECISION;
static constexpr uint64_t LN2_MICRO = 693147;
static constexpr uint64_t DECAY_PRECISION = dgb::coin::weight_decay::DECAY_PRECISION;
static constexpr uint64_t DECAY_SCALE = dgb::coin::weight_decay::DECAY_SCALE;

uint32_t half_life = std::max(PoolConfig::chain_length() / 4, uint32_t(1));
uint64_t decay_per = DECAY_SCALE - (DECAY_SCALE * LN2_MICRO) / (uint64_t(1000000) * half_life);
uint32_t half_life = dgb::coin::weight_decay::half_life(PoolConfig::chain_length());
uint64_t decay_per = dgb::coin::weight_decay::decay_per_share(PoolConfig::chain_length());

int32_t share_count = 0;
uint64_t decay_fp = DECAY_SCALE;
Expand Down
84 changes: 84 additions & 0 deletions src/impl/dgb/test/share_weight_decay_test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -85,3 +85,87 @@ TEST(DgbWeightDecay, DecayedAttemptsZeroAndIdentity) {
EXPECT_EQ(wd::decayed_attempts(0, wd::DECAY_SCALE), uint64_t(0));
EXPECT_EQ(wd::decayed_attempts(12345, wd::DECAY_SCALE), uint64_t(12345)); // x1.0
}

// ===================================================================
// #450 VALUE-INVARIANCE KAT -- proves the share_tracker.hpp rewire onto
// the SSOT is byte-identical to the prior open-coded arithmetic.
//
// Each of the three rewired sites (init_decay_table, get_v36_decayed_
// cumulative_weights, dump_v36_pplns_walk) previously computed:
// half_life = max(chain_length / 4, 1)
// decay_per = SCALE - (SCALE * 693147) / (1e6 * half_life)
// decay_fp_{d+1} = mul128_shift(decay_fp_d, decay_per, 40)
// decayed_att = (att * decay_fp) >> 40
// inline. The rewire routes half_life/decay_per/constants through the SSOT
// while leaving the mul128_shift decay_fp walk + the uint288 hot-path
// widening open-coded (the consensus/wire bytes). This KAT re-evaluates
// the FULL decayed-cumulative-weight vector via the OLD literal expressions
// and via the SSOT helpers over a depth + chain-length sweep and asserts
// equality -- the proof the merge needs.
//
// mul128_shift is reproduced verbatim from share_tracker.hpp; it is the
// SAME function on both arms (unchanged by the rewire), so it cancels and
// the comparison isolates exactly what moved into the SSOT.
namespace {
inline uint64_t mul128_shift_ref(uint64_t a, uint64_t b, unsigned shift) {
return static_cast<uint64_t>((static_cast<__uint128_t>(a) * b) >> shift);
}

// OLD open-coded constants (pre-rewire literals).
constexpr uint64_t OLD_SCALE = uint64_t(1) << 40;
constexpr uint64_t OLD_LN2 = 693147;
inline uint32_t old_half_life(uint32_t cl) { return std::max(cl / 4, uint32_t(1)); }
inline uint64_t old_decay_per(uint32_t cl) {
return OLD_SCALE - (OLD_SCALE * OLD_LN2) / (uint64_t(1000000) * old_half_life(cl));
}
} // namespace

TEST(DgbWeightDecay, RewireConstantsValueInvariant) {
for (uint32_t cl : {8640u, 2880u, 3600u, 720u, 100u, 8u, 4u, 3u, 1u, 0u}) {
EXPECT_EQ(old_half_life(cl), wd::half_life(cl)) << "half_life cl=" << cl;
EXPECT_EQ(old_decay_per(cl), wd::decay_per_share(cl)) << "decay_per cl=" << cl;
EXPECT_EQ(wd::DECAY_SCALE, OLD_SCALE);
EXPECT_EQ(wd::DECAY_PRECISION, 40u);
}
}

// Full decayed-cumulative-weight vector: old expressions vs SSOT helpers.
TEST(DgbWeightDecay, DecayedCumulativeWeightVectorInvariant) {
for (uint32_t cl : {8640u, 2880u, 720u, 4u}) {
const uint64_t old_per = old_decay_per(cl);
const uint64_t new_per = wd::decay_per_share(cl);
ASSERT_EQ(old_per, new_per);

uint64_t old_fp = OLD_SCALE;
uint64_t new_fp = wd::DECAY_SCALE;
uint64_t old_cum_addr = 0, new_cum_addr = 0;
uint64_t old_cum_total = 0, new_cum_total = 0;

const int depths = 64;
for (int d = 0; d < depths; ++d) {
for (uint64_t att : {uint64_t(65535), uint64_t(1000), uint64_t(7), uint64_t(0)}) {
for (uint32_t don : {0u, 1u, 100u, 65535u}) {
uint64_t old_dec = (att * old_fp) >> 40;
uint64_t old_addr = old_dec * (65535 - don);
uint64_t old_don = old_dec * don;
uint64_t new_dec = wd::decayed_attempts(att, new_fp);
uint64_t new_addr = new_dec * (65535 - don);
uint64_t new_don = new_dec * don;

EXPECT_EQ(old_dec, new_dec) << "cl=" << cl << " d=" << d << " att=" << att;
EXPECT_EQ(old_addr, new_addr);
EXPECT_EQ(old_don, new_don);

old_cum_addr += old_addr; new_cum_addr += new_addr;
old_cum_total += old_addr + old_don;
new_cum_total += new_addr + new_don;
}
}
old_fp = mul128_shift_ref(old_fp, old_per, 40);
new_fp = mul128_shift_ref(new_fp, new_per, 40);
ASSERT_EQ(old_fp, new_fp) << "decay_fp drift cl=" << cl << " d=" << d;
}
EXPECT_EQ(old_cum_addr, new_cum_addr) << "cumulative addr weight cl=" << cl;
EXPECT_EQ(old_cum_total, new_cum_total) << "cumulative total weight cl=" << cl;
}
}
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