From 8aefe626a90e6d1b76177e72ae6b384158ae0369 Mon Sep 17 00:00:00 2001
From: "A. Unique TensorFlower" <gardener@tensorflow.org>
Date: Wed, 16 Sep 2020 12:41:59 -0700
Subject: [PATCH] Fix micro string formatting bug.  Properly handle float
 fractions with no leading zeros.

PiperOrigin-RevId: 332065497
Change-Id: I2e8470ccd7082eee220268593ea3a100888567d1
---
 tensorflow/lite/micro/micro_string.cc      | 14 ++++++++------
 tensorflow/lite/micro/micro_string_test.cc |  9 +++++++++
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/tensorflow/lite/micro/micro_string.cc b/tensorflow/lite/micro/micro_string.cc
index 95a0ae156ae..ad769f69b0e 100644
--- a/tensorflow/lite/micro/micro_string.cc
+++ b/tensorflow/lite/micro/micro_string.cc
@@ -192,13 +192,15 @@ char* FastFloatToBufferLeft(float f, char* buffer) {
   // works properly.
   *current = '0';
 
-  // Shift fraction values and prepent zeros.
-  for (int i = 0; i < fraction_digits; i++) {
-    current--;
-    *(current + leading_zeros) = *current;
-    *current = '0';
+  // Shift fraction values and prepend zeros if necessary.
+  if (leading_zeros != 0) {
+    for (int i = 0; i < fraction_digits; i++) {
+      current--;
+      *(current + leading_zeros) = *current;
+      *current = '0';
+    }
+    current += kMaxFractionalDigits;
   }
-  current += kMaxFractionalDigits;
 
   // Truncate trailing zeros for cleaner logs. Ensure we leave at least one
   // fractional character for the case when scaled_fraction is 0.
diff --git a/tensorflow/lite/micro/micro_string_test.cc b/tensorflow/lite/micro/micro_string_test.cc
index 400f908f97f..f69812c5a9e 100644
--- a/tensorflow/lite/micro/micro_string_test.cc
+++ b/tensorflow/lite/micro/micro_string_test.cc
@@ -120,6 +120,15 @@ TF_LITE_MICRO_TEST(FloatFormatShouldPrintFractionCorrectly) {
   TF_LITE_MICRO_EXPECT_STRING_EQ(golden, buffer);
 }
 
+TF_LITE_MICRO_TEST(FloatFormatShouldPrintFractionCorrectlyNoLeadingZeros) {
+  const int kBufferLen = 24;
+  char buffer[kBufferLen];
+  const char golden[] = "Float: 1.6332993*2^-1";
+  int bytes_written = MicroSnprintf(buffer, kBufferLen, "Float: %f", 0.816650);
+  TF_LITE_MICRO_EXPECT_EQ(static_cast<int>(sizeof(golden)), bytes_written);
+  TF_LITE_MICRO_EXPECT_STRING_EQ(golden, buffer);
+}
+
 TF_LITE_MICRO_TEST(StringFormatOverrunShouldTruncate) {
   const int kBufferLen = 10;
   char buffer[kBufferLen];