diff --git a/src/include/harpfloat.h b/src/include/harpfloat.h
new file mode 100644
index 00000000..5fc50ebb
--- /dev/null
+++ b/src/include/harpfloat.h
@@ -0,0 +1,123 @@
+/*******************************************************************************
+ HARPtools by Chad D. Kersey, Summer 2011
+*******************************************************************************/
+#include <math.h>
+#include <stdlib.h>
+
+#include "types.h"
+
+#ifdef DEBUG
+#include <iostream>
+
+#define DEBUGMSG(x) do { \
+  std::cout << __FILE__ << ':' <<__LINE__ << ": " << x << '\n'; \
+} while(0)
+#else
+#define DEBUGMSG(x) do { } while(0)
+#endif
+
+namespace Harp {
+  // This class serves to handle the strange-precision floating point that can 
+  // crop up in HARP. 
+  class Float {
+  public:
+    Float(Word_u bin, Size n): sz(n) {
+      DEBUGMSG("Float(0x" << std::hex << bin << ", " << std::dec << n << ')');
+      
+      bool sign(bin >> (n*8 - 1));
+      
+      Size expSz;
+      if (n < 4) {
+        expSz = 5;
+      } else if (n < 8) {
+        expSz = 8;
+      } else {
+        expSz = 11;
+      }
+
+      Size sigSz = n*8 - expSz - 1;
+
+      DEBUGMSG("  exp: " << std::dec << expSz <<
+               " bits, sig: " << std::dec << sigSz << " bits.");
+
+      int exp = (bin >> sigSz) & ((1<<expSz) - 1);
+      Word_u sig = bin & ((1llu<<sigSz) - 1);
+      DEBUGMSG("  sig=" << std::dec << sig << " exp=" << exp);
+
+      if (exp == 0) {
+        // Subnormal 
+        d = sig / pow(2, ((1<<(expSz-1))-2)) / pow(2, sigSz);
+        DEBUGMSG("  Denorm.");
+      } else if (exp == ((1<<expSz) - 1)) {
+        // Infinity
+        d = HUGE_VAL;
+        DEBUGMSG("  Inf.");
+      } else {
+        // Normalized, implied 1.
+        exp -= (1<<(expSz - 1)) - 1;
+        d = pow(2.0, exp - int(sigSz)) * double((1ll << sigSz) + sig);
+        DEBUGMSG("  Norm, exp=" << exp);
+      }
+
+      if (sign) d = -d;
+
+      DEBUGMSG("Set to " << d);
+    }
+
+    Float(double d, Size n): sz(n), d(d) { DEBUGMSG("Float(double, size)"); }
+
+    operator Word_u() {
+      DEBUGMSG("Float -> Word_u: " << d);
+      Size expSz;
+      if (sz < 4) {
+        expSz = 5;
+      } else if (sz < 8) {
+        expSz = 8;
+      } else {
+        expSz = 11;
+      }
+
+      Size sigSz = 8*sz - expSz - 1;
+
+      bool sign(d < 0);
+
+      bool inf(isinf(d)), zero(d == 0.0);
+      int exp;
+
+      if (!inf && !zero) exp = floor(log2(fabs(d)));
+
+      Word_u rval;
+      if (inf) {
+        // Infinity
+        DEBUGMSG("  Inf.");
+        rval = ((1llu<<expSz)-1llu)<<sigSz;
+      } else if (!zero && abs(exp) < (1<<(expSz-1)) - 1) {
+        // Normalized with implied 1.
+        Word_u sig = (fabs(d) * pow(2.0, -exp) - 1.0) * pow(2.0, sigSz);
+        DEBUGMSG("  Norm, exp=" << exp << ", sig=" << sig);
+        rval = ((((exp + ((1llu<<(expSz-1)) - 1llu))
+                                          &((1llu<<expSz)-1llu)))<<sigSz) | sig;
+      } else if (!zero && exp > -(1<<(expSz-1)) - sigSz) {
+        // Subnormal number.
+        Word_u sig = round(fabs(d)*pow(2.0,((1<<(expSz-1))-2))*pow(2.0, sigSz));
+        DEBUGMSG("  Denorm, exp=" << exp << ", sig=" << sig);
+        rval = sig;
+      } else {
+        // Zero.
+        rval = 0;
+      }
+      
+      if (sign) rval |= 1llu<<(sz*8 - 1);
+
+      DEBUGMSG("  Returning 0x" << std::hex << rval);
+
+      return rval;
+    }
+
+    operator double() { DEBUGMSG("Float->double " << d); return d; }
+
+  private:
+    double d;
+    Size sz;
+  };
+};
diff --git a/src/include/instruction.h b/src/include/instruction.h
index d809a6d5..b99f3861 100644
--- a/src/include/instruction.h
+++ b/src/include/instruction.h
@@ -29,7 +29,8 @@ namespace Harp {
                   ANDI, ORI, XORI, ADDI, SUBI, MULI, DIVI, MODI, SHLI, SHRI,
                   JALI, JALR, JMPI, JMPR, CLONE, JALIS, JALRS, 
                   JMPRT, LD, ST, LDI, RTOP, ANDP, ORP, XORP, NOTP, ISNEG, 
-                  ISZERO, HALT, TRAP, JMPRU, SKEP, RETI, TLBRM };
+                  ISZERO, HALT, TRAP, JMPRU, SKEP, RETI, TLBRM,
+                  ITOF, FTOI, FADD, FSUB, FMUL, FDIV, FNEG };
     enum ArgClass {
       AC_NONE, AC_2REG, AC_2IMM, AC_3REG, AC_3PREG, AC_3IMM, AC_3REGSRC, 
       AC_1IMM, AC_1REG, AC_3IMMSRC, AC_PREG_REG, AC_2PREG
diff --git a/src/include/types.h b/src/include/types.h
index e71f018e..ae14cd8b 100644
--- a/src/include/types.h
+++ b/src/include/types.h
@@ -12,8 +12,8 @@ namespace Harp {
   typedef uint64_t Word_u;
   typedef int64_t  Word_s;
 
-  typedef Word     Addr;
-  typedef Word     Size;
+  typedef Word_u   Addr;
+  typedef Word_u   Size;
 
   typedef unsigned RegNum;
   typedef unsigned ThdNum;
diff --git a/src/instruction.cpp b/src/instruction.cpp
index 0311498b..20b8109a 100644
--- a/src/instruction.cpp
+++ b/src/instruction.cpp
@@ -7,6 +7,7 @@
 #include "include/instruction.h"
 #include "include/obj.h"
 #include "include/core.h"
+#include "include/harpfloat.h"
 
 using namespace Harp;
 using namespace std;
@@ -19,7 +20,8 @@ const char *Instruction::opStrings[] = {
   "ori", "xori", "addi", "subi", "muli", "divi", "modi", "shli", "shri", 
   "jali", "jalr", "jmpi", "jmpr", "clone", "jalis", "jalrs",
   "jmprt", "ld", "st", "ldi", "rtop", "andp", "orp", "xorp", "notp", 
-  "isneg", "iszero", "halt", "trap", "jmpru", "skep", "reti", "tlbrm", 0
+  "isneg", "iszero", "halt", "trap", "jmpru", "skep", "reti", "tlbrm",
+  "itof", "ftoi", "fadd", "fsub", "fmul", "fdiv", "fneg", 0
 };
 
 const bool Instruction::isControlFlow[] = {
@@ -28,7 +30,8 @@ const bool Instruction::isControlFlow[] = {
   false, false, false, false, false, false, false, false, false,
   true,  true,  true,  true,  true,  true,  true,
   true,  false, false, false, false, false, false, false, false,
-  false, false, false, false, true,  false, true,  false
+  false, false, false, false, true,  false, true,  false,
+  false, false, false, false, false, false, false
 };
 
 const bool Instruction::relAddress[] = {
@@ -37,7 +40,8 @@ const bool Instruction::relAddress[] = {
   false, false, false, false, false, false, false, false, false,
   true,  false, true,  false, false, true,  false,
   false, false, false, false, false, false, false, false, false,
-  false, false, false, false, false, false, false, false
+  false, false, false, false, false, false, false, false,
+  false, false, false, false, false, false, false
 };
 
 const bool Instruction::allSrcArgs[] = {
@@ -46,7 +50,8 @@ const bool Instruction::allSrcArgs[] = {
   false, false, false, false, false, false, false, false, false,
   false, false, true,  true,  false, false, false,
   true,  false, true,  false, false, false, false, false, false,
-  false, false, false, false, true,  true,  false, false
+  false, false, false, false, true,  true,  false, false,
+  false, false, false, false, false, false, false
 };
 
 const bool Instruction::privileged[] = {
@@ -55,7 +60,8 @@ const bool Instruction::privileged[] = {
   false, false, false, false, false, false, false, false, false,
   false, false, false, false, false, false, false,
   false, false, false, false, false, false, false, false, false,
-  false, false, true,  false, true,  true,  true,  true
+  false, false, true,  false, true,  true,  true,  true,
+  false, false, false, false, false, false, false
 };
 
 const Instruction::ArgClass Instruction::argClasses[] = {
@@ -68,7 +74,8 @@ const Instruction::ArgClass Instruction::argClasses[] = {
   AC_1REG, AC_3IMM, AC_3IMMSRC, AC_2IMM, AC_PREG_REG, AC_3PREG, AC_3PREG, 
   AC_3PREG, AC_2PREG,
   AC_PREG_REG, AC_PREG_REG, AC_NONE, AC_NONE, AC_1REG, AC_1REG, AC_NONE,
-  AC_1REG
+  AC_1REG,
+  AC_2REG, AC_2REG, AC_3REG, AC_3REG, AC_3REG, AC_3REG, AC_2REG
 };
 
 ostream &Harp::operator<<(ostream& os, Instruction &inst) {
@@ -110,6 +117,7 @@ void Instruction::executeOn(Core &c) {
   }
 
   Size nextActiveThreads = c.activeThreads;
+  Size wordSz = c.a.getWordSize();
 
   for (Size t = 0; t < c.activeThreads; t++) {
     vector<Word> &reg(c.reg[t]);
@@ -192,7 +200,7 @@ void Instruction::executeOn(Core &c) {
                  break;
       case NOTP: pReg[pdest] = !(pReg[psrc[0]]);
                  break;
-      case ISNEG: pReg[pdest] = (1ll<<(c.a.getWordSize()*8 - 1))&reg[rsrc[0]];
+      case ISNEG: pReg[pdest] = (1ll<<(wordSz*8 - 1))&reg[rsrc[0]];
                   break;
       case HALT: c.activeThreads = 0;
                  nextActiveThreads = 0;
@@ -213,6 +221,24 @@ void Instruction::executeOn(Core &c) {
                    c.pc = c.shadowPc;
                  }
                  break;
+      case ITOF: reg[rdest] = Float(double(reg[rsrc[0]]), wordSz);
+                 break; 
+      case FTOI: reg[rdest] = Word_s(double(Float(reg[rsrc[0]], wordSz)));
+                 break;
+      case FNEG: reg[rdest] = Float(-double(Float(reg[rsrc[0]],wordSz)),wordSz);
+                 break;
+      case FADD: reg[rdest] = Float(double(Float(reg[rsrc[0]], wordSz)) +
+                                    double(Float(reg[rsrc[1]], wordSz)),wordSz);
+                 break;
+      case FSUB: reg[rdest] = Float(double(Float(reg[rsrc[0]], wordSz)) -
+                                    double(Float(reg[rsrc[1]], wordSz)),wordSz);
+                 break;
+      case FMUL: reg[rdest] = Float(double(Float(reg[rsrc[0]], wordSz)) *
+                                    double(Float(reg[rsrc[1]], wordSz)),wordSz);
+                 break;
+      case FDIV: reg[rdest] = Float(double(Float(reg[rsrc[0]], wordSz)) /
+                                    double(Float(reg[rsrc[1]], wordSz)),wordSz);
+                 break;
       default:
         cout << "ERROR: Unsupported instruction: " << *this << "\n";
         exit(1);
diff --git a/src/unit_test/float_test.cpp b/src/unit_test/float_test.cpp
new file mode 100644
index 00000000..8d5169a1
--- /dev/null
+++ b/src/unit_test/float_test.cpp
@@ -0,0 +1,49 @@
+#include "include/harpfloat.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+using namespace Harp;
+using namespace std;
+
+static void try_val(double d, Size sz) {
+  Float f(d, sz);
+  Word w(f);
+  double e(Float(w, sz));
+  printf("%uB: %g -> 0x%llx -> %g\n", sz, d, (unsigned long long)w, e);
+}
+
+int main() {
+  /* Loop over available integer sizes. */
+  unsigned randseed(time(NULL));
+  for (unsigned sz = 1; sz <= 8; sz++) {
+    srand(randseed);
+
+    /* First test some random ordinary numbers and their conversions. */
+    for (unsigned i = 0; i < 2; i++) {
+      int n = rand() - RAND_MAX/2;
+      double d = n * 0.0000001;
+      try_val(d, sz);
+    }
+
+    /* Next, let's try +/- infinity. */
+    for (unsigned i = 0; i < 2; i++) {
+      double d(i?HUGE_VAL:-HUGE_VAL);
+      try_val(d, sz);
+    }
+
+    /* Last, let's try some random subnormal numbers and their conversions. */
+    double mote;
+    if (sz < 4) mote = pow(2, int(-14 - (sz*8 - 6)));
+    else if (sz < 8) mote = pow(2, int(-126 - (sz*8 - 9)));
+    else mote = pow(2, int(-1022 - (sz*8 - 12)));
+    for (unsigned i = 0; i < 2; i++) {
+      int n = rand()%256;
+      double d = n * mote;
+      try_val(d, sz);
+    }
+  }
+
+  return 0;
+}