From f4cd35d2edf3f7918afb1aef86915a4918f959d2 Mon Sep 17 00:00:00 2001
From: Doug Hoyte <doug@hcsw.org>
Date: Mon, 6 Mar 2023 00:30:24 -0500
Subject: [PATCH] wip

---
 src/xor.h | 86 +++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 55 insertions(+), 31 deletions(-)

diff --git a/src/xor.h b/src/xor.h
index 8f5a3c0..f0750eb 100644
--- a/src/xor.h
+++ b/src/xor.h
@@ -66,7 +66,8 @@ struct XorView {
         if (!ready) throw herr("xor view not ready");
 
         std::string output;
-        splitRange(elems.begin(), elems.end(), 0, "", 1678053147ULL, "", output);
+        uint64_t lastTimestampOut = 0;
+        splitRange(elems.begin(), elems.end(), 0, "", MAX_U64, "", lastTimestampOut, output);
         return output;
     }
 
@@ -76,15 +77,26 @@ struct XorView {
 
         std::string output;
         auto prevUpper = elems.begin();
+        uint64_t lastTimestampIn = 0;
+        uint64_t lastTimestampOut = 0;
+
+        auto decodeTimestampIn = [&](std::string_view &query){
+            uint64_t timestamp = decodeVarInt(query);
+            timestamp = timestamp == 0 ? MAX_U64 : timestamp - 1;
+            timestamp += lastTimestampIn;
+            if (timestamp < lastTimestampIn) timestamp = MAX_U64; // saturate
+            lastTimestampIn = timestamp;
+            return timestamp;
+        };
 
         while (query.size()) {
-            uint64_t lowerTimestamp = decodeVarInt(query);
+            uint64_t lowerTimestamp = decodeTimestampIn(query);
             uint64_t lowerLength = decodeVarInt(query);
             if (lowerLength > idSize) throw herr("lower too long");
             auto lowerKeyRaw = getBytes(query, lowerLength);
             XorElem lowerKey(lowerTimestamp, lowerKeyRaw);
 
-            uint64_t upperTimestamp = decodeVarInt(query);
+            uint64_t upperTimestamp = decodeTimestampIn(query);
             uint64_t upperLength = decodeVarInt(query);
             if (upperLength > idSize) throw herr("upper too long");
             auto upperKeyRaw = getBytes(query, upperLength);
@@ -102,7 +114,7 @@ struct XorView {
                 XorElem ourXorSet;
                 for (auto i = lower; i < upper; ++i) ourXorSet ^= *i;
 
-                if (theirXorSet.getId(idSize) != ourXorSet.getId(idSize)) splitRange(lower, upper, lowerTimestamp, lowerKeyRaw, upperTimestamp, upperKeyRaw, output);
+                if (theirXorSet.getId(idSize) != ourXorSet.getId(idSize)) splitRange(lower, upper, lowerTimestamp, lowerKeyRaw, upperTimestamp, upperKeyRaw, lastTimestampOut, output);
             } else if (mode >= 8) {
                 flat_hash_map<XorElem, bool> theirElems;
                 for (uint64_t i = 0; i < mode - 8; i++) {
@@ -136,7 +148,45 @@ struct XorView {
 
   private:
 
-    void splitRange(std::vector<XorElem>::iterator lower, std::vector<XorElem>::iterator upper, uint64_t lowerTimestamp, const std::string &lowerKey, uint64_t upperTimestamp, const std::string &upperKey, std::string &output) {
+    void splitRange(std::vector<XorElem>::iterator lower, std::vector<XorElem>::iterator upper, uint64_t lowerTimestamp, const std::string &lowerKey, uint64_t upperTimestamp, const std::string &upperKey, uint64_t &lastTimestampOut, std::string &output) {
+        auto encodeTimestampOut = [&](uint64_t timestamp){
+            if (timestamp == MAX_U64) {
+                lastTimestampOut = MAX_U64;
+                return encodeVarInt(0);
+            }
+
+            uint64_t temp = timestamp;
+            timestamp -= lastTimestampOut;
+            lastTimestampOut = temp;
+            return encodeVarInt(timestamp + 1);
+        };
+
+        auto appendBoundKey = [&](uint64_t t, std::string k, std::string &output) {
+            output += encodeTimestampOut(t);
+            output += encodeVarInt(k.size());
+            output += k;
+        };
+
+        auto appendMinimalBoundKey = [&](const XorElem &curr, const XorElem &prev, std::string &output) {
+            output += encodeTimestampOut(curr.timestamp);
+
+            if (curr.timestamp != prev.timestamp) {
+                output += encodeVarInt(0);
+            } else {
+                uint64_t sharedPrefixBytes = 0;
+                auto currKey = curr.getId(idSize);
+                auto prevKey = prev.getId(idSize);
+
+                for (uint64_t i = 0; i < idSize; i++) {
+                    if (currKey[i] != prevKey[i]) break;
+                    sharedPrefixBytes++;
+                }
+
+                output += encodeVarInt(sharedPrefixBytes + 1);
+                output += currKey.substr(0, sharedPrefixBytes + 1);
+            }
+        };
+
         // Split our range
         uint64_t numElems = upper - lower;
         const uint64_t buckets = 16;
@@ -169,32 +219,6 @@ struct XorView {
             }
         }
     }
-
-    void appendBoundKey(uint64_t t, std::string k, std::string &output) {
-        output += encodeVarInt(t);
-        output += encodeVarInt(k.size());
-        output += k;
-    }
-
-    void appendMinimalBoundKey(const XorElem &curr, const XorElem &prev, std::string &output) {
-        output += encodeVarInt(curr.timestamp);
-
-        if (curr.timestamp != prev.timestamp) {
-            output += encodeVarInt(0);
-        } else {
-            uint64_t sharedPrefixBytes = 0;
-            auto currKey = curr.getId(idSize);
-            auto prevKey = prev.getId(idSize);
-
-            for (uint64_t i = 0; i < idSize; i++) {
-                if (currKey[i] != prevKey[i]) break;
-                sharedPrefixBytes++;
-            }
-
-            output += encodeVarInt(sharedPrefixBytes + 1);
-            output += currKey.substr(0, sharedPrefixBytes + 1);
-        }
-    }
 };