From c5adf9e4a59c429e3c02a078d033d5fda4c6a3ba Mon Sep 17 00:00:00 2001
From: Daniel Lemire <lemire@gmail.com>
Date: Mon, 11 Jan 2021 11:22:00 -0500
Subject: [PATCH] Fix truncate flag.

---
 include/fast_float/ascii_number.h | 26 +++++++++++++++++++++-----
 tests/basictest.cpp               | 10 ++++++----
 2 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/include/fast_float/ascii_number.h b/include/fast_float/ascii_number.h
index 75432a3..e8d12ee 100644
--- a/include/fast_float/ascii_number.h
+++ b/include/fast_float/ascii_number.h
@@ -249,6 +249,27 @@ fastfloat_really_inline decimal parse_decimal(const char *p, const char *pend) n
     }
     answer.decimal_point = int32_t(first_after_period - p);
   }
+  // We want num_digits to be the number of significant digits, excluding
+  // leading *and* trailing zeros! Otherwise the truncated flag later is
+  // going to be misleading.
+  if(answer.num_digits > 0) {
+    // We potentially need the answer.num_digits > 0 guard because we
+    // prune leading zeros. So with answer.num_digits > 0, we know that
+    // we have at least one non-zero digit.
+    const char *preverse = p - 1;
+    int32_t trailing_zeros = 0;
+    while ((*preverse == '0') || (*preverse == '.')) {
+      if(*preverse == '0') { trailing_zeros++; };
+      --preverse;
+    }
+    answer.decimal_point += trailing_zeros;
+    answer.num_digits -= uint32_t(trailing_zeros);
+    answer.decimal_point += int32_t(answer.num_digits);
+  }
+  if(answer.num_digits > max_digits) {
+    answer.truncated = true;
+    answer.num_digits = max_digits;
+  }
   if ((p != pend) && (('e' == *p) || ('E' == *p))) {
     ++p;
     bool neg_exp = false;
@@ -268,11 +289,6 @@ fastfloat_really_inline decimal parse_decimal(const char *p, const char *pend) n
     }
     answer.decimal_point += (neg_exp ? -exp_number : exp_number);
   }
-  answer.decimal_point += int32_t(answer.num_digits);
-  if(answer.num_digits > max_digits) {
-    answer.truncated = true;
-    answer.num_digits = max_digits;
-  }
   // In very rare cases, we may have fewer than 19 digits, we want to be able to reliably
   // assume that all digits up to max_digit_without_overflow have been initialized.
   for(uint32_t i = answer.num_digits; i < max_digit_without_overflow; i++) { answer.digits[i] = 0; }
diff --git a/tests/basictest.cpp b/tests/basictest.cpp
index 100815b..66ba9c6 100644
--- a/tests/basictest.cpp
+++ b/tests/basictest.cpp
@@ -294,10 +294,8 @@ TEST_CASE("64bit.inf") {
 }
 
 TEST_CASE("64bit.general") {
-  verify("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125", 0x1.2ced2f1aa2833p+0);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced2f1aa2833p+0);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced2f1aa2833p+0);
-  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced2f1aa2833p+0);
+  verify("9007199254740993.0", 0x1p+53);
+  verify(append_zeros("9007199254740993.0",1000), 0x1p+53);
   verify("10000000000000000000", 0x1.158e460913dp+63);
   verify("10000000000000000000000000000001000000000000", 0x1.cb2d6f618c879p+142);
   verify("10000000000000000000000000000000000000000001", 0x1.cb2d6f618c879p+142);
@@ -369,9 +367,13 @@ TEST_CASE("32bit.inf") {
 
 TEST_CASE("32bit.general") {
   verify("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125", 0x1.2ced3p+0f);
+  verify("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125e-38", 0x1.fffff8p-127f);
   verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655), 0x1.2ced3p+0f);
   verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656), 0x1.2ced3p+0f);
   verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000), 0x1.2ced3p+0f);
+  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",655) + "e-38", 0x1.fffff8p-127f);
+  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",656) + "e-38", 0x1.fffff8p-127f);
+  verify(append_zeros("1.1754941406275178592461758986628081843312458647327962400313859427181746759860647699724722770042717456817626953125",1000) + "e-38", 0x1.fffff8p-127f);
   verify32(1.00000006e+09f);
   verify32(1.4012984643e-45f);
   verify32(1.1754942107e-38f);