Add assertions to check preconditions of functions and unsigned integer arithmetic

Author: abolz

include/rapidjson/internal/diyfp.h

@@ -141,6 +141,9 @@ struct DiyFp {
             double d;
             uint64_t u64;
         }u;
+        RAPIDJSON_ASSERT(f <= kDpHiddenBit + kDpSignificandMask);
+        RAPIDJSON_ASSERT(e >= kDpDenormalExponent);
+        RAPIDJSON_ASSERT(e < kDpMaxExponent);
         const uint64_t be = (e == kDpDenormalExponent && (f & kDpHiddenBit) == 0) ? 0 : 
             static_cast<uint64_t>(e + kDpExponentBias);
         u.u64 = (f & kDpSignificandMask) | (be << kDpSignificandSize);
@@ -220,6 +223,7 @@ inline DiyFp GetCachedPowerByIndex(size_t index) {
         641,   667,   694,   720,   747,   774,   800,   827,   853,   880,
         907,   933,   960,   986,  1013,  1039,  1066
     };
+    RAPIDJSON_ASSERT(index < 87);
     return DiyFp(kCachedPowers_F[index], kCachedPowers_E[index]);
 }
 
@@ -238,10 +242,11 @@ inline DiyFp GetCachedPower(int e, int* K) {
 }
 
 inline DiyFp GetCachedPower10(int exp, int *outExp) {
-     unsigned index = (static_cast<unsigned>(exp) + 348u) / 8u;
-     *outExp = -348 + static_cast<int>(index) * 8;
-     return GetCachedPowerByIndex(index);
- }
+    RAPIDJSON_ASSERT(exp >= -348);
+    unsigned index = static_cast<unsigned>(exp + 348) / 8u;
+    *outExp = -348 + static_cast<int>(index) * 8;
+    return GetCachedPowerByIndex(index);
+}
 
 #ifdef __GNUC__
 RAPIDJSON_DIAG_POP

include/rapidjson/internal/strtod.h

@@ -233,12 +233,14 @@ inline double StrtodFullPrecision(double d, int p, const char* decimals, size_t
     while (*decimals == '0' && length > 1) {
         length--;
         decimals++;
+        RAPIDJSON_ASSERT(decimalPosition > 0);
         decimalPosition--;
     }
 
     // Trim trailing zeros
     while (decimals[length - 1] == '0' && length > 1) {
         length--;
+        RAPIDJSON_ASSERT(decimalPosition > 0);
         decimalPosition--;
         exp++;
     }
@@ -248,6 +250,7 @@ inline double StrtodFullPrecision(double d, int p, const char* decimals, size_t
     if (static_cast<int>(length) > kMaxDecimalDigit) {
         int delta = (static_cast<int>(length) - kMaxDecimalDigit);
         exp += delta;
+        RAPIDJSON_ASSERT(decimalPosition > static_cast<unsigned>(delta));
         decimalPosition -= static_cast<unsigned>(delta);
         length = kMaxDecimalDigit;
     }