diff --git a/csrc/float_fix.cc b/csrc/float_fix.cc
index 8f5188b2..a488d5c2 100644
--- a/csrc/float_fix.cc
+++ b/csrc/float_fix.cc
@@ -1,21 +1,59 @@
 #include <assert.h>
 #include <cinttypes>
 #include <cstdio>
+#include <cstdlib>
 #include <iostream>
 #include <fstream>
-#include <sstream>
 
 
-// returns the bits in x[high:low] in the lowest positions
+// float_fix - Scott Beamer, 2015
+
+// This program post-processes commit logs from rocket-chip to make it easier
+// to diff against commit logs from spike. Rocket internally uses recoded
+// floating point numbers, but this is normally hidden because the commit
+// logging tool unrecodes (undoes the recoding) those numbers. This tool is for
+// the corner case (single-precision float stored and loaded from memory as a
+// double) when the commit logging tool is unable to recode properly on its
+// own. Given both a rocket commit log (already processed by comlog) and commit
+// log from spike, this tools attempts to fix that corner case. This tool will
+// only overwrite the log to hold the unrecoded float if that change will cause
+// it to match with the spike log (conservative).
+
+
+// Returns the bits in x[high:low] in the lowest positions
 uint64_t BitRange(uint64_t x, int high, int low) {
   int high_gap = 64 - high;
   return x << high_gap >> (low + high_gap);
 }
 
 
-// will "unrecode" a single float within a double
-// uses magic numbers since can only handle float
-// logic from berkeley-hardfloat/src/main/scala/recodedFloatNToFloatN.scala
+// Returns uint64_t from the hex encoding within s offset by index
+uint64_t UIntFromHexSubstring(std::string s, int index) {
+  uint64_t x = strtoull(s.c_str() + index, nullptr, 16);
+  assert(errno == 0);
+  return x;
+}
+
+
+// Is commit line for a fld instruction?
+bool LineIsFLDInst(std::string line) {
+  uint32_t inst_bits = UIntFromHexSubstring(line, 22);
+  uint32_t width_field = (inst_bits >> 12) & 7;
+  uint32_t opcode_field = inst_bits & 127;
+  return (width_field == 3) && (opcode_field == 7);
+}
+
+
+// Is number possibly a recoded float inside double (upper 31 bits set)?
+bool NestedFloatPossible(uint64_t raw_input) {
+  const uint64_t mask = 0xfffffffe00000000;
+  return (raw_input & mask) == mask;
+}
+
+
+// Unrecodes a single float within a double
+//   uses magic numbers since can only handle float
+//   logic from berkeley-hardfloat/src/main/scala/recodedFloatNToFloatN.scala
 uint64_t UnrecodeFloatFromDouble(uint64_t raw_input) {
   uint64_t recoded_float = raw_input & 0x1ffffffff;  // lower 33 bits
   uint64_t sign = BitRange(recoded_float, 31, 31);
@@ -39,23 +77,17 @@ uint64_t UnrecodeFloatFromDouble(uint64_t raw_input) {
                       is_subnormal ? subnormal_sig_out : 0;
 
   uint64_t raw_output64 = (sign << 63) | (exp_out << 23) | sig_out;
-  // make sure nothing leaked over the top
-  assert((raw_output64 & 0xffffffff00000000) == uint64_t(0));
+  // assert((raw_output64 & 0xffffffff00000000) == uint64_t(0));
+  // If this is not a recoded float, this will return gibberish, however,
+  // the output will not match spike and thus the replacement will not happen.
   return raw_output64;
 }
 
 
-// checks if possibly recoded float inside double (upper 31 bits set)
-bool NestedFloatPossible(uint64_t raw_input) {
-  const uint64_t mask = 0xfffffffe00000000;
-  return (raw_input & mask) == mask;
-}
-
-
-// best effort at replacing the float writeback with unrecoded version
-// will only replace if (all of following met):
+// Best effort at replacing the float writeback with unrecoded version
+//   will only replace if (all of following met):
 //   - log lines differ between rocket and lspike
-//   - log line contains a floating point inst
+//   - log line is a fld instruction
 //   - unrecoding the writeback data as a single float makes them match
 void DiffAndFix(std::string rocket_filename, std::string lspike_filename) {
   std::ifstream rocket_log(rocket_filename);
@@ -68,17 +100,12 @@ void DiffAndFix(std::string rocket_filename, std::string lspike_filename) {
     std::cout << "Couldn't open file " << lspike_filename << std::endl;
     std::exit(-2);
   }
-  std::stringstream ss;
-  ss << std::hex;
   std::string rocket_line, lspike_line;
-  while (getline(rocket_log,rocket_line) && getline(lspike_log,lspike_line)) {
-    if ((rocket_line != lspike_line) &&
-        (rocket_line.find(" f") != std::string::npos)) {
+  while (getline(rocket_log, rocket_line)) {
+    if (getline(lspike_log, lspike_line) && (rocket_line != lspike_line) &&
+        LineIsFLDInst(rocket_line)) {
       std::string fixed_line(rocket_line.c_str());  // deep copy
-      std::string fp_wb_str = fixed_line.substr(40, 16);
-      uint64_t raw_fp;
-      ss << fp_wb_str;
-      ss >> raw_fp;
+      uint64_t raw_fp = UIntFromHexSubstring(fixed_line, 40);
       if (NestedFloatPossible(raw_fp)) {
         snprintf(const_cast<char*>(fixed_line.data()) + 40, 17,
                  "%016" PRIx64, UnrecodeFloatFromDouble(raw_fp));
@@ -98,7 +125,6 @@ int main(int argc, char** argv) {
     std::cout << "Usage: float_fix rocket_output lspike_output" << std::endl;
     return -1;
   }
-  // std::cout << NestedFloatPossible(0xf0f0f0ff0f000000) << std::endl;
   DiffAndFix(std::string(argv[1]), std::string(argv[2]));
   return 0;
 }