From 73fcc40fa4382e2325be601bd85ebe258420e1ce Mon Sep 17 00:00:00 2001
From: pennae <github@quasiparticle.net>
Date: Fri, 31 Dec 2021 03:16:59 +0100
Subject: [PATCH] use boost::lexical_cast for string2*

this avoids one copy from `s` into `str`, and possibly another copy needed to
construct `s` at the call site. lexical_cast is also more efficient in general.
---
 src/libutil/util.hh | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index d08f42826..7da60b310 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -11,6 +11,8 @@
 #include <unistd.h>
 #include <signal.h>
 
+#include <boost/lexical_cast.hpp>
+
 #include <atomic>
 #include <functional>
 #include <map>
@@ -417,21 +419,21 @@ bool statusOk(int status);
 
 /* Parse a string into an integer. */
 template<class N>
-std::optional<N> string2Int(const std::string & s)
+std::optional<N> string2Int(const std::string_view s)
 {
     if (s.substr(0, 1) == "-" && !std::numeric_limits<N>::is_signed)
         return std::nullopt;
-    std::istringstream str(s);
-    N n;
-    str >> n;
-    if (str && str.get() == EOF) return n;
-    return std::nullopt;
+    try {
+        return boost::lexical_cast<N>(s.data(), s.size());
+    } catch (const boost::bad_lexical_cast &) {
+        return std::nullopt;
+    }
 }
 
 /* Like string2Int(), but support an optional suffix 'K', 'M', 'G' or
    'T' denoting a binary unit prefix. */
 template<class N>
-N string2IntWithUnitPrefix(std::string s)
+N string2IntWithUnitPrefix(std::string_view s)
 {
     N multiplier = 1;
     if (!s.empty()) {
@@ -442,7 +444,7 @@ N string2IntWithUnitPrefix(std::string s)
             else if (u == 'G') multiplier = 1ULL << 30;
             else if (u == 'T') multiplier = 1ULL << 40;
             else throw UsageError("invalid unit specifier '%1%'", u);
-            s.resize(s.size() - 1);
+            s.remove_suffix(1);
         }
     }
     if (auto n = string2Int<N>(s))
@@ -452,13 +454,13 @@ N string2IntWithUnitPrefix(std::string s)
 
 /* Parse a string into a float. */
 template<class N>
-std::optional<N> string2Float(const string & s)
+std::optional<N> string2Float(const std::string_view s)
 {
-    std::istringstream str(s);
-    N n;
-    str >> n;
-    if (str && str.get() == EOF) return n;
-    return std::nullopt;
+    try {
+        return boost::lexical_cast<N>(s.data(), s.size());
+    } catch (const boost::bad_lexical_cast &) {
+        return std::nullopt;
+    }
 }