diff --git a/src/pow/tromp/equi.h b/src/pow/tromp/equi.h
new file mode 100644
index 000000000..7a0355a73
--- /dev/null
+++ b/src/pow/tromp/equi.h
@@ -0,0 +1,129 @@
+// Equihash solver
+// Copyright (c) 2016-2016 John Tromp
+
+#include "blake/blake2.h"
+#ifdef __APPLE__
+#include "osx_barrier.h"
+#include <machine/endian.h>
+#include <libkern/OSByteOrder.h>
+#define htole32(x) OSSwapHostToLittleInt32(x)
+#else
+#include <endian.h>
+#endif
+#include <stdint.h> // for types uint32_t,uint64_t
+#include <string.h> // for functions memset
+#include <stdlib.h> // for function qsort
+
+typedef uint32_t u32;
+typedef unsigned char uchar;
+
+// algorithm parameters, prefixed with W to reduce include file conflicts
+
+#ifndef WN
+#define WN	200
+#endif
+
+#ifndef WK
+#define WK	9
+#endif
+
+#define NDIGITS		(WK+1)
+#define DIGITBITS	(WN/(NDIGITS))
+
+static const u32 PROOFSIZE = 1<<WK;
+static const u32 BASE = 1<<DIGITBITS;
+static const u32 NHASHES = 2*BASE;
+static const u32 HASHESPERBLAKE = 512/WN;
+static const u32 HASHOUT = HASHESPERBLAKE*WN/8;
+
+typedef u32 proof[PROOFSIZE];
+
+void setheader(blake2b_state *ctx, const char *header, const u32 headerlen, u32 nce) {
+  uint32_t le_N = htole32(WN);
+  uint32_t le_K = htole32(WK);
+  uchar personal[] = "ZcashPoW01230123";
+  memcpy(personal+8,  &le_N, 4);
+  memcpy(personal+12, &le_K, 4);
+  blake2b_param P[1];
+  P->digest_length = HASHOUT;
+  P->key_length    = 0;
+  P->fanout        = 1;
+  P->depth         = 1;
+  P->leaf_length   = 0;
+  P->node_offset   = 0;
+  P->node_depth    = 0;
+  P->inner_length  = 0;
+  memset(P->reserved, 0, sizeof(P->reserved));
+  memset(P->salt,     0, sizeof(P->salt));
+  memcpy(P->personal, (const uint8_t *)personal, 16);
+  blake2b_init_param(ctx, P);
+  blake2b_update(ctx, (const uchar *)header, headerlen);
+  uchar nonce[32];
+  memset(nonce, 0, 32);
+  uint32_t le_nonce = htole32(nce);
+  memcpy(nonce,  &le_nonce, 4);
+  blake2b_update(ctx, nonce, 32);
+}
+
+enum verify_code { POW_OK, POW_DUPLICATE, POW_OUT_OF_ORDER, POW_NONZERO_XOR };
+const char *errstr[] = { "OK", "duplicate index", "indices out of order", "nonzero xor" };
+
+void genhash(blake2b_state *ctx, u32 idx, uchar *hash) {
+  blake2b_state state = *ctx;
+  u32 leb = htole32(idx / HASHESPERBLAKE);
+  blake2b_update(&state, (uchar *)&leb, sizeof(u32));
+  uchar blakehash[HASHOUT];
+  blake2b_final(&state, blakehash, HASHOUT);
+  memcpy(hash, blakehash + (idx % HASHESPERBLAKE) * WN/8, WN/8);
+}
+
+int verifyrec(blake2b_state *ctx, u32 *indices, uchar *hash, int r) {
+  if (r == 0) {
+    genhash(ctx, *indices, hash);
+    return POW_OK;
+  }
+  u32 *indices1 = indices + (1 << (r-1));
+  if (*indices >= *indices1)
+    return POW_OUT_OF_ORDER;
+  uchar hash0[WN/8], hash1[WN/8];
+  int vrf0 = verifyrec(ctx, indices,  hash0, r-1);
+  if (vrf0 != POW_OK)
+    return vrf0;
+  int vrf1 = verifyrec(ctx, indices1, hash1, r-1);
+  if (vrf1 != POW_OK)
+    return vrf1;
+  for (int i=0; i < WN/8; i++)
+    hash[i] = hash0[i] ^ hash1[i];
+  int i, b = r * DIGITBITS;
+  for (i = 0; i < b/8; i++)
+    if (hash[i])
+      return POW_NONZERO_XOR;
+  if ((b%8) && hash[i] >> (8-(b%8)))
+    return POW_NONZERO_XOR;
+  return POW_OK;
+}
+
+int compu32(const void *pa, const void *pb) {
+  u32 a = *(u32 *)pa, b = *(u32 *)pb;
+  return a<b ? -1 : a==b ? 0 : +1;
+}
+
+bool duped(proof prf) {
+  proof sortprf;
+  memcpy(sortprf, prf, sizeof(proof));
+  qsort(sortprf, PROOFSIZE, sizeof(u32), &compu32);
+  for (u32 i=1; i<PROOFSIZE; i++)
+    if (sortprf[i] <= sortprf[i-1])
+      return true;
+  return false;
+}
+
+// verify Wagner conditions
+int verify(u32 indices[PROOFSIZE], const char *header, const u32 headerlen, const u32 nonce) {
+  if (duped(indices))
+    return POW_DUPLICATE;
+  blake2b_state ctx;
+  setheader(&ctx, header, headerlen, nonce);
+  uchar hash[WN/8];
+  return verifyrec(&ctx, indices, hash, WK);
+}
diff --git a/src/pow/tromp/equi_miner.h b/src/pow/tromp/equi_miner.h
new file mode 100644
index 000000000..db2b83098
--- /dev/null
+++ b/src/pow/tromp/equi_miner.h
@@ -0,0 +1,644 @@
+// Equihash solver
+// Copyright (c) 2016 John Tromp
+
+// Fix N, K, such that n = N/(k+1) is integer
+// Fix M = 2^{n+1} hashes each of length N bits,
+// H_0, ... , H_{M-1}, generated fom (n+1)-bit indices.
+// Problem: find binary tree on 2^K distinct indices,
+// for which the exclusive-or of leaf hashes is all 0s.
+// Additionally, it should satisfy the Wagner conditions:
+// for each height i subtree, the exclusive-or
+// of its 2^i corresponding hashes starts with i*n 0 bits,
+// and for i>0 the leftmost leaf of its left subtree
+// is less than the leftmost leaf of its right subtree
+
+// The algorithm below solves this by maintaining the trees
+// in a graph of K layers, each split into buckets
+// with buckets indexed by the first n-RESTBITS bits following
+// the i*n 0s, each bucket having 4 * 2^RESTBITS slots,
+// twice the number of subtrees expected to land there.
+
+#include "equi.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <assert.h>
+
+typedef uint16_t u16;
+typedef uint64_t u64;
+
+#ifdef ATOMIC
+#include <atomic>
+typedef std::atomic<u32> au32;
+#else
+typedef u32 au32;
+#endif
+
+#ifndef RESTBITS
+#define RESTBITS	8
+#endif
+
+// 2_log of number of buckets
+#define BUCKBITS (DIGITBITS-RESTBITS)
+
+#ifndef SAVEMEM
+#if RESTBITS == 4
+// can't save memory in such small buckets
+#define SAVEMEM 1
+#elif RESTBITS >= 8
+// take advantage of law of large numbers (sum of 2^8 random numbers)
+// this reduces (200,9) memory to under 144MB, with negligible discarding
+#define SAVEMEM 9/14
+#endif
+#endif
+
+// number of buckets
+static const u32 NBUCKETS = 1<<BUCKBITS;
+// 2_log of number of slots per bucket
+static const u32 SLOTBITS = RESTBITS+1+1;
+static const u32 SLOTRANGE = 1<<SLOTBITS;
+static const u32 SLOTMSB = 1<<(SLOTBITS-1);
+// number of slots per bucket
+static const u32 NSLOTS = SLOTRANGE * SAVEMEM;
+// number of per-xhash slots
+static const u32 XFULL = 16;
+// SLOTBITS mask
+static const u32 SLOTMASK = SLOTRANGE-1;
+// number of possible values of xhash (rest of n) bits
+static const u32 NRESTS = 1<<RESTBITS;
+// number of blocks of hashes extracted from single 512 bit blake2b output
+static const u32 NBLOCKS = (NHASHES+HASHESPERBLAKE-1)/HASHESPERBLAKE;
+// nothing larger found in 100000 runs
+static const u32 MAXSOLS = 8;
+
+// tree node identifying its children as two different slots in
+// a bucket on previous layer with the same rest bits (x-tra hash)
+struct tree {
+  u32 bid_s0_s1; // manual bitfields
+
+  tree(const u32 idx) {
+    bid_s0_s1 = idx;
+  }
+  tree(const u32 bid, const u32 s0, const u32 s1) {
+#ifdef SLOTDIFF
+    u32 ds10 = (s1 - s0) & SLOTMASK;
+    if (ds10 & SLOTMSB) {
+      bid_s0_s1 = (((bid << SLOTBITS) | s1) << (SLOTBITS-1)) | (SLOTMASK & ~ds10);
+    } else {
+      bid_s0_s1 = (((bid << SLOTBITS) | s0) << (SLOTBITS-1)) | (ds10 - 1);
+    }
+#else
+    bid_s0_s1 = (((bid << SLOTBITS) | s0) << SLOTBITS) | s1;
+#endif
+  }
+  u32 getindex() const {
+    return bid_s0_s1;
+  }
+  u32 bucketid() const {
+#ifdef SLOTDIFF
+    return bid_s0_s1 >> (2 * SLOTBITS - 1);
+#else
+    return bid_s0_s1 >> (2 * SLOTBITS);
+#endif
+  }
+  u32 slotid0() const {
+#ifdef SLOTDIFF
+    return (bid_s0_s1 >> (SLOTBITS-1)) & SLOTMASK;
+#else
+    return (bid_s0_s1 >> SLOTBITS) & SLOTMASK;
+#endif
+  }
+  u32 slotid1() const {
+#ifdef SLOTDIFF
+    return (slotid0() + 1 + (bid_s0_s1 & (SLOTMASK>>1))) & SLOTMASK;
+#else
+    return bid_s0_s1 & SLOTMASK;
+#endif
+  }
+};
+
+union hashunit {
+  u32 word;
+  uchar bytes[sizeof(u32)];
+};
+
+#define WORDS(bits)	((bits + 31) / 32)
+#define HASHWORDS0 WORDS(WN - DIGITBITS + RESTBITS)
+#define HASHWORDS1 WORDS(WN - 2*DIGITBITS + RESTBITS)
+
+struct slot0 {
+  tree attr;
+  hashunit hash[HASHWORDS0];
+};
+
+struct slot1 {
+  tree attr;
+  hashunit hash[HASHWORDS1];
+};
+
+// a bucket is NSLOTS treenodes
+typedef slot0 bucket0[NSLOTS];
+typedef slot1 bucket1[NSLOTS];
+// the N-bit hash consists of K+1 n-bit "digits"
+// each of which corresponds to a layer of NBUCKETS buckets
+typedef bucket0 digit0[NBUCKETS];
+typedef bucket1 digit1[NBUCKETS];
+
+// size (in bytes) of hash in round 0 <= r < WK
+u32 hashsize(const u32 r) {
+  const u32 hashbits = WN - (r+1) * DIGITBITS + RESTBITS;
+  return (hashbits + 7) / 8;
+}
+
+u32 hashwords(u32 bytes) {
+  return (bytes + 3) / 4;
+}
+
+// manages hash and tree data
+struct htalloc {
+  u32 *heap0;
+  u32 *heap1;
+  bucket0 *trees0[(WK+1)/2];
+  bucket1 *trees1[WK/2];
+  u32 alloced;
+  htalloc() {
+    alloced = 0;
+  }
+  void alloctrees() {
+// optimize xenoncat's fixed memory layout, avoiding any waste
+// digit  trees  hashes  trees hashes
+// 0      0 A A A A A A   . . . . . .
+// 1      0 A A A A A A   1 B B B B B
+// 2      0 2 C C C C C   1 B B B B B
+// 3      0 2 C C C C C   1 3 D D D D
+// 4      0 2 4 E E E E   1 3 D D D D
+// 5      0 2 4 E E E E   1 3 5 F F F
+// 6      0 2 4 6 . G G   1 3 5 F F F
+// 7      0 2 4 6 . G G   1 3 5 7 H H
+// 8      0 2 4 6 8 . I   1 3 5 7 H H
+    assert(DIGITBITS >= 16); // ensures hashes shorten by 1 unit every 2 digits
+    heap0 = (u32 *)alloc(1, sizeof(digit0));
+    heap1 = (u32 *)alloc(1, sizeof(digit1));
+    for (int r=0; r<WK; r++)
+      if ((r&1) == 0)
+        trees0[r/2]  = (bucket0 *)(heap0 + r/2);
+      else
+        trees1[r/2]  = (bucket1 *)(heap1 + r/2);
+  }
+  void dealloctrees() {
+    free(heap0);
+    free(heap1);
+  }
+  void *alloc(const u32 n, const u32 sz) {
+    void *mem  = calloc(n, sz);
+    assert(mem);
+    alloced += n * sz;
+    return mem;
+  }
+};
+
+typedef au32 bsizes[NBUCKETS];
+
+u32 min(const u32 a, const u32 b) {
+  return a < b ? a : b;
+}
+
+struct equi {
+  blake2b_state blake_ctx;
+  htalloc hta;
+  bsizes *nslots; // PUT IN BUCKET STRUCT
+  proof *sols;
+  au32 nsols;
+  u32 nthreads;
+  u32 xfull;
+  u32 hfull;
+  u32 bfull;
+  pthread_barrier_t barry;
+  equi(const u32 n_threads) {
+    assert(sizeof(hashunit) == 4);
+    nthreads = n_threads;
+    const int err = pthread_barrier_init(&barry, NULL, nthreads);
+    assert(!err);
+    hta.alloctrees();
+    nslots = (bsizes *)hta.alloc(2 * NBUCKETS, sizeof(au32));
+    sols   =  (proof *)hta.alloc(MAXSOLS, sizeof(proof));
+  }
+  ~equi() {
+    hta.dealloctrees();
+    free(nslots);
+    free(sols);
+  }
+  void setnonce(const char *header, const u32 headerlen, const u32 nonce) {
+    setheader(&blake_ctx, header, headerlen, nonce);
+    memset(nslots, 0, NBUCKETS * sizeof(au32)); // only nslots[0] needs zeroing
+    nsols = 0;
+  }
+  u32 getslot(const u32 r, const u32 bucketi) {
+#ifdef ATOMIC
+    return std::atomic_fetch_add_explicit(&nslots[r&1][bucketi], 1U, std::memory_order_relaxed);
+#else
+    return nslots[r&1][bucketi]++;
+#endif
+  }
+  u32 getnslots(const u32 r, const u32 bid) { // SHOULD BE METHOD IN BUCKET STRUCT
+    au32 &nslot = nslots[r&1][bid];
+    const u32 n = min(nslot, NSLOTS);
+    nslot = 0;
+    return n;
+  }
+  void orderindices(u32 *indices, u32 size) {
+    if (indices[0] > indices[size]) {
+      for (u32 i=0; i < size; i++) {
+        const u32 tmp = indices[i];
+        indices[i] = indices[size+i];
+        indices[size+i] = tmp;
+      }
+    }
+  }
+  void listindices0(u32 r, const tree t, u32 *indices) {
+    if (r == 0) {
+      *indices = t.getindex();
+      return;
+    }
+    const bucket1 &buck = hta.trees1[--r/2][t.bucketid()];
+    const u32 size = 1 << r;
+    u32 *indices1 = indices + size;
+    listindices1(r, buck[t.slotid0()].attr, indices);
+    listindices1(r, buck[t.slotid1()].attr, indices1);
+    orderindices(indices, size);
+  }
+  void listindices1(u32 r, const tree t, u32 *indices) {
+    const bucket0 &buck = hta.trees0[--r/2][t.bucketid()];
+    const u32 size = 1 << r;
+    u32 *indices1 = indices + size;
+    listindices0(r, buck[t.slotid0()].attr, indices);
+    listindices0(r, buck[t.slotid1()].attr, indices1);
+    orderindices(indices, size);
+  }
+  void candidate(const tree t) {
+    proof prf;
+    listindices1(WK, t, prf); // assume WK odd
+    qsort(prf, PROOFSIZE, sizeof(u32), &compu32);
+    for (u32 i=1; i<PROOFSIZE; i++)
+      if (prf[i] <= prf[i-1])
+        return;
+#ifdef ATOMIC
+    u32 soli = std::atomic_fetch_add_explicit(&nsols, 1U, std::memory_order_relaxed);
+#else
+    u32 soli = nsols++;
+#endif
+    if (soli < MAXSOLS)
+      listindices1(WK, t, sols[soli]); // assume WK odd
+  }
+  void showbsizes(u32 r) {
+#if defined(HIST) || defined(SPARK) || defined(LOGSPARK)
+    u32 binsizes[65];
+    memset(binsizes, 0, 65 * sizeof(u32));
+    for (u32 bucketid = 0; bucketid < NBUCKETS; bucketid++) {
+      u32 bsize = min(nslots[r&1][bucketid], NSLOTS) >> (SLOTBITS-6);
+      binsizes[bsize]++;
+    }
+    for (u32 i=0; i < 65; i++) {
+#ifdef HIST
+      printf(" %d:%d", i, binsizes[i]);
+#else
+#ifdef SPARK
+      u32 sparks = binsizes[i] / SPARKSCALE;
+#else
+      u32 sparks = 0;
+      for (u32 bs = binsizes[i]; bs; bs >>= 1) sparks++;
+      sparks = sparks * 7 / SPARKSCALE;
+#endif
+      printf("\342\226%c", '\201' + sparks);
+#endif
+    }
+    printf("\n");
+#endif
+  }
+
+  struct htlayout {
+    htalloc hta;
+    u32 prevhashunits;
+    u32 nexthashunits;
+    u32 dunits;
+    u32 prevbo;
+    u32 nextbo;
+  
+    htlayout(equi *eq, u32 r): hta(eq->hta), prevhashunits(0), dunits(0) {
+      u32 nexthashbytes = hashsize(r);
+      nexthashunits = hashwords(nexthashbytes);
+      prevbo = 0;
+      nextbo = nexthashunits * sizeof(hashunit) - nexthashbytes; // 0-3
+      if (r) {
+        u32 prevhashbytes = hashsize(r-1);
+        prevhashunits = hashwords(prevhashbytes);
+        prevbo = prevhashunits * sizeof(hashunit) - prevhashbytes; // 0-3
+        dunits = prevhashunits - nexthashunits;
+      }
+    }
+    u32 getxhash0(const slot0* pslot) const {
+#if WN == 200 && RESTBITS == 4
+      return pslot->hash->bytes[prevbo] >> 4;
+#elif WN == 200 && RESTBITS == 8
+      return (pslot->hash->bytes[prevbo] & 0xf) << 4 | pslot->hash->bytes[prevbo+1] >> 4;
+#elif WN == 200 && RESTBITS == 9
+      return (pslot->hash->bytes[prevbo] & 0x1f) << 4 | pslot->hash->bytes[prevbo+1] >> 4;
+#elif WN == 144 && RESTBITS == 4
+      return pslot->hash->bytes[prevbo] & 0xf;
+#else
+#error non implemented
+#endif
+    }
+    u32 getxhash1(const slot1* pslot) const {
+#if WN == 200 && RESTBITS == 4
+      return pslot->hash->bytes[prevbo] & 0xf;
+#elif WN == 200 && RESTBITS == 8
+      return pslot->hash->bytes[prevbo];
+#elif WN == 200 && RESTBITS == 9
+      return (pslot->hash->bytes[prevbo]&1) << 8 | pslot->hash->bytes[prevbo+1];
+#elif WN == 144 && RESTBITS == 4
+      return pslot->hash->bytes[prevbo] & 0xf;
+#else
+#error non implemented
+#endif
+    }
+    bool equal(const hashunit *hash0, const hashunit *hash1) const {
+      return hash0[prevhashunits-1].word == hash1[prevhashunits-1].word;
+    }
+  };
+
+  struct collisiondata {
+#ifdef XBITMAP
+#if NSLOTS > 64
+#error cant use XBITMAP with more than 64 slots
+#endif
+    u64 xhashmap[NRESTS];
+    u64 xmap;
+#else
+#if RESTBITS <= 6
+    typedef uchar xslot;
+#else
+    typedef u16 xslot;
+#endif
+    xslot nxhashslots[NRESTS];
+    xslot xhashslots[NRESTS][XFULL];
+    xslot *xx;
+    u32 n0;
+    u32 n1;
+#endif
+    u32 s0;
+
+    void clear() {
+#ifdef XBITMAP
+      memset(xhashmap, 0, NRESTS * sizeof(u64));
+#else
+      memset(nxhashslots, 0, NRESTS * sizeof(xslot));
+#endif
+    }
+    bool addslot(u32 s1, u32 xh) {
+#ifdef XBITMAP
+      xmap = xhashmap[xh];
+      xhashmap[xh] |= (u64)1 << s1;
+      s0 = -1;
+      return true;
+#else
+      n1 = (u32)nxhashslots[xh]++;
+      if (n1 >= XFULL)
+        return false;
+      xx = xhashslots[xh];
+      xx[n1] = s1;
+      n0 = 0;
+      return true;
+#endif
+    }
+    bool nextcollision() const {
+#ifdef XBITMAP
+      return xmap != 0;
+#else
+      return n0 < n1;
+#endif
+    }
+    u32 slot() {
+#ifdef XBITMAP
+      const u32 ffs = __builtin_ffsll(xmap);
+      s0 += ffs; xmap >>= ffs;
+      return s0;
+#else
+      return (u32)xx[n0++];
+#endif
+    }
+  };
+
+  void digit0(const u32 id) {
+    uchar hash[HASHOUT];
+    blake2b_state state;
+    htlayout htl(this, 0);
+    const u32 hashbytes = hashsize(0);
+    for (u32 block = id; block < NBLOCKS; block += nthreads) {
+      state = blake_ctx;
+      u32 leb = htole32(block);
+      blake2b_update(&state, (uchar *)&leb, sizeof(u32));
+      blake2b_final(&state, hash, HASHOUT);
+      for (u32 i = 0; i<HASHESPERBLAKE; i++) {
+        const uchar *ph = hash + i * WN/8;
+#if BUCKBITS == 16 && RESTBITS == 4
+        const u32 bucketid = ((u32)ph[0] << 8) | ph[1];
+#elif BUCKBITS == 12 && RESTBITS == 8
+        const u32 bucketid = ((u32)ph[0] << 4) | ph[1] >> 4;
+#elif BUCKBITS == 11 && RESTBITS == 9
+        const u32 bucketid = ((u32)ph[0] << 3) | ph[1] >> 5;
+#elif BUCKBITS == 20 && RESTBITS == 4
+        const u32 bucketid = ((((u32)ph[0] << 8) | ph[1]) << 4) | ph[2] >> 4;
+#elif BUCKBITS == 12 && RESTBITS == 4
+        const u32 bucketid = ((u32)ph[0] << 4) | ph[1] >> 4;
+        const u32 xhash = ph[1] & 0xf;
+#else
+#error not implemented
+#endif
+        const u32 slot = getslot(0, bucketid);
+        if (slot >= NSLOTS) {
+          bfull++;
+          continue;
+        }
+        slot0 &s = hta.trees0[0][bucketid][slot];
+        s.attr = tree(block * HASHESPERBLAKE + i);
+        memcpy(s.hash->bytes+htl.nextbo, ph+WN/8-hashbytes, hashbytes);
+      }
+    }
+  }
+  
+  void digitodd(const u32 r, const u32 id) {
+    htlayout htl(this, r);
+    collisiondata cd;
+    for (u32 bucketid=id; bucketid < NBUCKETS; bucketid += nthreads) {
+      cd.clear();
+      slot0 *buck = htl.hta.trees0[(r-1)/2][bucketid]; // optimize by updating previous buck?!
+      u32 bsize = getnslots(r-1, bucketid);       // optimize by putting bucketsize with block?!
+      for (u32 s1 = 0; s1 < bsize; s1++) {
+        const slot0 *pslot1 = buck + s1;          // optimize by updating previous pslot1?!
+        if (!cd.addslot(s1, htl.getxhash0(pslot1))) {
+          xfull++;
+          continue;
+        }
+        for (; cd.nextcollision(); ) {
+          const u32 s0 = cd.slot();
+          const slot0 *pslot0 = buck + s0;
+          if (htl.equal(pslot0->hash, pslot1->hash)) {
+            hfull++;
+            continue;
+          }
+          u32 xorbucketid;
+          const uchar *bytes0 = pslot0->hash->bytes, *bytes1 = pslot1->hash->bytes;
+#if WN == 200 && BUCKBITS == 12 && RESTBITS == 8
+          xorbucketid = (((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) & 0xf) << 8)
+                             | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]);
+#elif WN == 200 && BUCKBITS == 11 && RESTBITS == 9
+          xorbucketid = (((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) & 0xf) << 7)
+                             | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]) >> 1;
+#elif WN == 144 && BUCKBITS == 20 && RESTBITS == 4
+          xorbucketid = ((((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) << 8)
+                              | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2])) << 4)
+                              | (bytes0[htl.prevbo+3] ^ bytes1[htl.prevbo+3]) >> 4;
+#elif WN == 96 && BUCKBITS == 12 && RESTBITS == 4
+          xorbucketid = ((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) << 4)
+                            | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]) >> 4;
+#else
+#error not implemented
+#endif
+          const u32 xorslot = getslot(r, xorbucketid);
+          if (xorslot >= NSLOTS) {
+            bfull++;
+            continue;
+          }
+          slot1 &xs = htl.hta.trees1[r/2][xorbucketid][xorslot];
+          xs.attr = tree(bucketid, s0, s1);
+          for (u32 i=htl.dunits; i < htl.prevhashunits; i++)
+            xs.hash[i-htl.dunits].word = pslot0->hash[i].word ^ pslot1->hash[i].word;
+        }
+      }
+    }
+  }
+  
+  void digiteven(const u32 r, const u32 id) {
+    htlayout htl(this, r);
+    collisiondata cd;
+    for (u32 bucketid=id; bucketid < NBUCKETS; bucketid += nthreads) {
+      cd.clear();
+      slot1 *buck = htl.hta.trees1[(r-1)/2][bucketid]; // OPTIMIZE BY UPDATING PREVIOUS
+      u32 bsize = getnslots(r-1, bucketid);
+      for (u32 s1 = 0; s1 < bsize; s1++) {
+        const slot1 *pslot1 = buck + s1;          // OPTIMIZE BY UPDATING PREVIOUS
+        if (!cd.addslot(s1, htl.getxhash1(pslot1))) {
+          xfull++;
+          continue;
+        }
+        for (; cd.nextcollision(); ) {
+          const u32 s0 = cd.slot();
+          const slot1 *pslot0 = buck + s0;
+          if (htl.equal(pslot0->hash, pslot1->hash)) {
+            hfull++;
+            continue;
+          }
+          u32 xorbucketid;
+          const uchar *bytes0 = pslot0->hash->bytes, *bytes1 = pslot1->hash->bytes;
+#if WN == 200 && BUCKBITS == 12 && RESTBITS == 8
+          xorbucketid = ((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) << 4)
+                            | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]) >> 4;
+#elif WN == 200 && BUCKBITS == 11 && RESTBITS == 9
+          xorbucketid = ((u32)(bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]) << 3)
+                            | (bytes0[htl.prevbo+3] ^ bytes1[htl.prevbo+3]) >> 5;
+#elif WN == 144 && BUCKBITS == 20 && RESTBITS == 4
+          xorbucketid = ((((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) << 8)
+                              | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2])) << 4)
+                              | (bytes0[htl.prevbo+3] ^ bytes1[htl.prevbo+3]) >> 4;
+#elif WN == 96 && BUCKBITS == 12 && RESTBITS == 4
+          xorbucketid = ((u32)(bytes0[htl.prevbo+1] ^ bytes1[htl.prevbo+1]) << 4)
+                            | (bytes0[htl.prevbo+2] ^ bytes1[htl.prevbo+2]) >> 4;
+#else
+#error not implemented
+#endif
+          const u32 xorslot = getslot(r, xorbucketid);
+          if (xorslot >= NSLOTS) {
+            bfull++;
+            continue;
+          }
+          slot0 &xs = htl.hta.trees0[r/2][xorbucketid][xorslot];
+          xs.attr = tree(bucketid, s0, s1);
+          for (u32 i=htl.dunits; i < htl.prevhashunits; i++)
+            xs.hash[i-htl.dunits].word = pslot0->hash[i].word ^ pslot1->hash[i].word;
+        }
+      }
+    }
+  }
+  
+  void digitK(const u32 id) {
+    collisiondata cd;
+    htlayout htl(this, WK);
+u32 nc = 0;
+    for (u32 bucketid = id; bucketid < NBUCKETS; bucketid += nthreads) {
+      cd.clear();
+      slot0 *buck = htl.hta.trees0[(WK-1)/2][bucketid];
+      u32 bsize = getnslots(WK-1, bucketid);
+      for (u32 s1 = 0; s1 < bsize; s1++) {
+        const slot0 *pslot1 = buck + s1;
+        if (!cd.addslot(s1, htl.getxhash0(pslot1))) // assume WK odd
+          continue;
+        for (; cd.nextcollision(); ) {
+          const u32 s0 = cd.slot();
+          if (htl.equal(buck[s0].hash, pslot1->hash))
+nc++,       candidate(tree(bucketid, s0, s1));
+        }
+      }
+    }
+printf(" %d candidates ", nc);
+  }
+};
+
+typedef struct {
+  u32 id;
+  pthread_t thread;
+  equi *eq;
+} thread_ctx;
+
+void barrier(pthread_barrier_t *barry) {
+  const int rc = pthread_barrier_wait(barry);
+  if (rc != 0 && rc != PTHREAD_BARRIER_SERIAL_THREAD) {
+    printf("Could not wait on barrier\n");
+    pthread_exit(NULL);
+  }
+}
+
+void *worker(void *vp) {
+  thread_ctx *tp = (thread_ctx *)vp;
+  equi *eq = tp->eq;
+
+  if (tp->id == 0)
+    printf("Digit 0\n");
+  barrier(&eq->barry);
+  eq->digit0(tp->id);
+  barrier(&eq->barry);
+  if (tp->id == 0) {
+    eq->xfull = eq->bfull = eq->hfull = 0;
+    eq->showbsizes(0);
+  }
+  barrier(&eq->barry);
+  for (u32 r = 1; r < WK; r++) {
+    if (tp->id == 0)
+      printf("Digit %d", r);
+    barrier(&eq->barry);
+    r&1 ? eq->digitodd(r, tp->id) : eq->digiteven(r, tp->id);
+    barrier(&eq->barry);
+    if (tp->id == 0) {
+      printf(" x%d b%d h%d\n", eq->xfull, eq->bfull, eq->hfull);
+      eq->xfull = eq->bfull = eq->hfull = 0;
+      eq->showbsizes(r);
+    }
+    barrier(&eq->barry);
+  }
+  if (tp->id == 0)
+    printf("Digit %d\n", WK);
+  eq->digitK(tp->id);
+  barrier(&eq->barry);
+  pthread_exit(NULL);
+  return 0;
+}
diff --git a/src/pow/tromp/osx_barrier.h b/src/pow/tromp/osx_barrier.h
new file mode 100644
index 000000000..da05b3552
--- /dev/null
+++ b/src/pow/tromp/osx_barrier.h
@@ -0,0 +1,70 @@
+#ifdef __APPLE__
+
+#ifndef PTHREAD_BARRIER_H_
+#define PTHREAD_BARRIER_H_
+
+#include <pthread.h>
+#include <errno.h>
+
+typedef int pthread_barrierattr_t;
+#define PTHREAD_BARRIER_SERIAL_THREAD 1
+
+typedef struct
+{
+    pthread_mutex_t mutex;
+    pthread_cond_t cond;
+    int count;
+    int tripCount;
+} pthread_barrier_t;
+
+
+int pthread_barrier_init(pthread_barrier_t *barrier, const pthread_barrierattr_t *attr, unsigned int count)
+{
+    if(count == 0)
+    {
+        errno = EINVAL;
+        return -1;
+    }
+    if(pthread_mutex_init(&barrier->mutex, 0) < 0)
+    {
+        return -1;
+    }
+    if(pthread_cond_init(&barrier->cond, 0) < 0)
+    {
+        pthread_mutex_destroy(&barrier->mutex);
+        return -1;
+    }
+    barrier->tripCount = count;
+    barrier->count = 0;
+
+    return 0;
+}
+
+int pthread_barrier_destroy(pthread_barrier_t *barrier)
+{
+    pthread_cond_destroy(&barrier->cond);
+    pthread_mutex_destroy(&barrier->mutex);
+    return 0;
+}
+
+int pthread_barrier_wait(pthread_barrier_t *barrier)
+{
+    pthread_mutex_lock(&barrier->mutex);
+    ++(barrier->count);
+    if(barrier->count >= barrier->tripCount)
+    {
+        barrier->count = 0;
+        pthread_cond_broadcast(&barrier->cond);
+        pthread_mutex_unlock(&barrier->mutex);
+        return PTHREAD_BARRIER_SERIAL_THREAD;
+    }
+    else
+    {
+        pthread_cond_wait(&barrier->cond, &(barrier->mutex));
+        pthread_mutex_unlock(&barrier->mutex);
+        return 0;
+    }
+}
+
+#endif // PTHREAD_BARRIER_H_
+#endif // __APPLE__