Removes Boost predicate.hpp dependency

This is a squashed commit that squashes the following commits:

This commit removes the `boost/algorithm/string/predicate.hpp` dependenc
from the project by replacing the function calls to `boost::algorithm::starts_with`
`boost::algorithm::ends_with` and `all` with respectively C++11'
`std::basic_string::front`, `std::basic_string::back`, `std::all_of` function calls

This commit replaces `boost::algorithm::is_digit` with  a locale independent isdigi
function, because the use of the standard library's `isdigit` and `std::isdigit
functions is discoraged in the developer notes

7 files changed, 39 insertions, 16 deletions

diff --git a/src/core_read.cpp b/src/core_read.cpp
index 067e1b91bd..7225ecc4bb 100644
--- a/src/core_read.cpp
+++ b/src/core_read.cpp
@@ -16,10 +16,11 @@
 #include <version.h>
 
 #include <boost/algorithm/string/classification.hpp>
-#include <boost/algorithm/string/predicate.hpp>
 #include <boost/algorithm/string/replace.hpp>
 #include <boost/algorithm/string/split.hpp>
 
+#include <algorithm>
+
 CScript ParseScript(const std::string& s)
 {
     CScript result;
@@ -54,20 +55,20 @@ CScript ParseScript(const std::string& s)
         {
             // Empty string, ignore. (boost::split given '' will return one word)
         }
-        else if (all(*w, boost::algorithm::is_digit()) ||
-            (boost::algorithm::starts_with(*w, "-") && all(std::string(w->begin()+1, w->end()), boost::algorithm::is_digit())))
+        else if (std::all_of(w->begin(), w->end(), ::IsDigit) ||
+            (w->front() == '-' && w->size() > 1 && std::all_of(w->begin()+1, w->end(), ::IsDigit)))
         {
             // Number
             int64_t n = atoi64(*w);
             result << n;
         }
-        else if (boost::algorithm::starts_with(*w, "0x") && (w->begin()+2 != w->end()) && IsHex(std::string(w->begin()+2, w->end())))
+        else if (w->substr(0,2) == "0x" && w->size() > 2 && IsHex(std::string(w->begin()+2, w->end())))
         {
             // Raw hex data, inserted NOT pushed onto stack:
             std::vector<unsigned char> raw = ParseHex(std::string(w->begin()+2, w->end()));
             result.insert(result.end(), raw.begin(), raw.end());
         }
-        else if (w->size() >= 2 && boost::algorithm::starts_with(*w, "'") && boost::algorithm::ends_with(*w, "'"))
+        else if (w->size() >= 2 && w->front() == '\'' && w->back() == '\'')
         {
             // Single-quoted string, pushed as data. NOTE: this is poor-man's
             // parsing, spaces/tabs/newlines in single-quoted strings won't work.
diff --git a/src/netbase.cpp b/src/netbase.cpp
index 4ce63cb0ec..607eb89573 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -20,7 +20,6 @@
 #endif
 
 #include <boost/algorithm/string/case_conv.hpp> // for to_lower()
-#include <boost/algorithm/string/predicate.hpp> // for startswith() and endswith()
 
 #if !defined(MSG_NOSIGNAL)
 #define MSG_NOSIGNAL 0
@@ -121,8 +120,7 @@ bool LookupHost(const char *pszName, std::vector<CNetAddr>& vIP, unsigned int nM
     std::string strHost(pszName);
     if (strHost.empty())
         return false;
-    if (boost::algorithm::starts_with(strHost, "[") && boost::algorithm::ends_with(strHost, "]"))
-    {
+    if (strHost.front() == '[' && strHost.back() == ']') {
         strHost = strHost.substr(1, strHost.size() - 2);
     }
 
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index d535f74e91..3661c762fc 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -806,6 +806,21 @@ BOOST_AUTO_TEST_CASE(gettime)
     BOOST_CHECK((GetTime() & ~0xFFFFFFFFLL) == 0);
 }
 
+BOOST_AUTO_TEST_CASE(test_IsDigit)
+{
+    BOOST_CHECK_EQUAL(IsDigit('0'), true);
+    BOOST_CHECK_EQUAL(IsDigit('1'), true);
+    BOOST_CHECK_EQUAL(IsDigit('8'), true);
+    BOOST_CHECK_EQUAL(IsDigit('9'), true);
+
+    BOOST_CHECK_EQUAL(IsDigit('0' - 1), false);
+    BOOST_CHECK_EQUAL(IsDigit('9' + 1), false);
+    BOOST_CHECK_EQUAL(IsDigit(0), false);
+    BOOST_CHECK_EQUAL(IsDigit(1), false);
+    BOOST_CHECK_EQUAL(IsDigit(8), false);
+    BOOST_CHECK_EQUAL(IsDigit(9), false);
+}
+
 BOOST_AUTO_TEST_CASE(test_ParseInt32)
 {
     int32_t n;
diff --git a/src/utilstrencodings.cpp b/src/utilstrencodings.cpp
index d1025fc7bf..c6927021cb 100644
--- a/src/utilstrencodings.cpp
+++ b/src/utilstrencodings.cpp
@@ -473,7 +473,7 @@ bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out)
             /* pass single 0 */
             ++ptr;
         } else if (val[ptr] >= '1' && val[ptr] <= '9') {
-            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+            while (ptr < end && IsDigit(val[ptr])) {
                 if (!ProcessMantissaDigit(val[ptr], mantissa, mantissa_tzeros))
                     return false; /* overflow */
                 ++ptr;
@@ -483,9 +483,9 @@ bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out)
     if (ptr < end && val[ptr] == '.')
     {
         ++ptr;
-        if (ptr < end && val[ptr] >= '0' && val[ptr] <= '9')
+        if (ptr < end && IsDigit(val[ptr]))
         {
-            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+            while (ptr < end && IsDigit(val[ptr])) {
                 if (!ProcessMantissaDigit(val[ptr], mantissa, mantissa_tzeros))
                     return false; /* overflow */
                 ++ptr;
@@ -502,8 +502,8 @@ bool ParseFixedPoint(const std::string &val, int decimals, int64_t *amount_out)
             exponent_sign = true;
             ++ptr;
         }
-        if (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
-            while (ptr < end && val[ptr] >= '0' && val[ptr] <= '9') {
+        if (ptr < end && IsDigit(val[ptr])) {
+            while (ptr < end && IsDigit(val[ptr])) {
                 if (exponent > (UPPER_BOUND / 10LL))
                     return false; /* overflow */
                 exponent = exponent * 10 + val[ptr] - '0';
diff --git a/src/utilstrencodings.h b/src/utilstrencodings.h
index 1c9cca90b2..47f9afba1c 100644
--- a/src/utilstrencodings.h
+++ b/src/utilstrencodings.h
@@ -62,6 +62,16 @@ int64_t atoi64(const std::string& str);
 int atoi(const std::string& str);
 
 /**
+ * Tests if the given character is a decimal digit.
+ * @param[in] c     character to test
+ * @return          true if the argument is a decimal digit; otherwise false.
+ */
+constexpr bool IsDigit(char c)
+{
+    return c >= '0' && c <= '9';
+}
+
+/**
  * Convert string to signed 32-bit integer with strict parse error feedback.
  * @returns true if the entire string could be parsed as valid integer,
  *   false if not the entire string could be parsed or when overflow or underflow occurred.
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
index 71fd973581..4e1f6548df 100644
--- a/src/wallet/rpcdump.cpp
+++ b/src/wallet/rpcdump.cpp
@@ -585,13 +585,13 @@ UniValue importwallet(const JSONRPCRequest& request)
                 std::string strLabel;
                 bool fLabel = true;
                 for (unsigned int nStr = 2; nStr < vstr.size(); nStr++) {
-                    if (boost::algorithm::starts_with(vstr[nStr], "#"))
+                    if (vstr[nStr].front() == '#')
                         break;
                     if (vstr[nStr] == "change=1")
                         fLabel = false;
                     if (vstr[nStr] == "reserve=1")
                         fLabel = false;
-                    if (boost::algorithm::starts_with(vstr[nStr], "label=")) {
+                    if (vstr[nStr].substr(0,6) == "label=") {
                         strLabel = DecodeDumpString(vstr[nStr].substr(6));
                         fLabel = true;
                     }
diff --git a/test/lint/lint-includes.sh b/test/lint/lint-includes.sh
index 2faaef8954..8f7a1fd76b 100755
--- a/test/lint/lint-includes.sh
+++ b/test/lint/lint-includes.sh
@@ -49,7 +49,6 @@ EXPECTED_BOOST_INCLUDES=(
     boost/algorithm/string.hpp
     boost/algorithm/string/case_conv.hpp
     boost/algorithm/string/classification.hpp
-    boost/algorithm/string/predicate.hpp
     boost/algorithm/string/replace.hpp
     boost/algorithm/string/split.hpp
     boost/bind.hpp