riscv/rocket-chip
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faster and more conservative float_fix

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This commit is contained in:
Scott Beamer 2015-09-15 17:19:02 -07:00
parent 7e25b1ce03
commit de81762f7c
1 changed files with 53 additions and 27 deletions
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74
csrc/float_fix.cc
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@ -1,19 +1,57 @@
#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
// 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) {
@ -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
// 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;
}