From 74744a9d5b9f4c6b5432dc1d3e8b6b0383887b48 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Wed, 13 Dec 2023 12:42:50 -0800
Subject: [PATCH 1/4] Speed up initLUT in flute.cpp by adding a specialized
 parser for decimal integers to replace sscanf(..., "%d%n", ...).

Signed-off-by: Rasmus Munk Larsen <rmlarsen@google.com>
---
 src/stt/src/flt/flute.cpp | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/src/stt/src/flt/flute.cpp b/src/stt/src/flt/flute.cpp
index 304855a0a78..9d65f1e9174 100644
--- a/src/stt/src/flt/flute.cpp
+++ b/src/stt/src/flt/flute.cpp
@@ -281,6 +281,27 @@ static unsigned char charNum(unsigned char c)
   return 0;
 }
 
+// Decodes a decimal integer from the string s.
+// Returns the decoded value in *value and returns
+// the number of characters read.
+inline const char* readDecimalInt(const char* s, int &value)
+{
+  value = 0;
+  bool negative = (*s == '-');
+  if (negative || *s == '+') {
+    ++s;
+  }
+  constexpr int zero_code = int('0');
+  while (*s >= '0' && *s <= '9') {
+    value = 10 * value + (int(*s) - zero_code);
+    ++s;
+  }
+  if (negative) {
+    value = -value;
+  }
+  return s;
+}
+
 // Init LUTs from base64 encoded string variables.
 static void initLUT(int to_d, LUT_TYPE LUT, NUMSOLN_TYPE numsoln)
 {
@@ -293,19 +314,21 @@ static void initLUT(int to_d, LUT_TYPE LUT, NUMSOLN_TYPE numsoln)
 #endif
 
   for (int d = 4; d <= to_d; d++) {
-    int char_cnt;
-    sscanf(pwv, "d=%d%n", &d, &char_cnt);
-    pwv += char_cnt + 1;
+    if (pwv[0] == 'd' && pwv[1] == '=') {
+      pwv = readDecimalInt(pwv + 2, d);
+    }
+    ++pwv;
 #if FLUTE_ROUTING == 1
-    sscanf(prt, "d=%d%n", &d, &char_cnt);
-    prt += char_cnt + 1;
+    if (pwv[0] == 'd' && pwv[1] == '=') {
+      pwv = readDecimalInt(pwv + 2, d);
+    }
+    ++pwv;
 #endif
     for (int k = 0; k < numgrp[d]; k++) {
       int ns = charNum(*pwv++);
       if (ns == 0) {  // same as some previous group
         int kk;
-        sscanf(pwv, "%d%n", &kk, &char_cnt);
-        pwv += char_cnt + 1;
+        pwv = readDecimalInt(pwv, kk) + 1;
         numsoln[d][k] = numsoln[d][kk];
         LUT[d][k] = LUT[d][kk];
       } else {

From e03f124924a667b44f4237ae474bb7f7469095e8 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Wed, 13 Dec 2023 15:57:06 -0800
Subject: [PATCH 2/4] clang-format.

Signed-off-by: Rasmus Munk Larsen <rmlarsen@google.com>
---
 src/stt/src/flt/flute.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/stt/src/flt/flute.cpp b/src/stt/src/flt/flute.cpp
index 9d65f1e9174..b13efb7b8de 100644
--- a/src/stt/src/flt/flute.cpp
+++ b/src/stt/src/flt/flute.cpp
@@ -284,7 +284,7 @@ static unsigned char charNum(unsigned char c)
 // Decodes a decimal integer from the string s.
 // Returns the decoded value in *value and returns
 // the number of characters read.
-inline const char* readDecimalInt(const char* s, int &value)
+inline const char* readDecimalInt(const char* s, int& value)
 {
   value = 0;
   bool negative = (*s == '-');

From 58c99eb87cddef70b579f6c5e9425e357e1fbbab Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Thu, 14 Dec 2023 15:25:37 -0800
Subject: [PATCH 3/4] Routing and regular path use different pointers.

Signed-off-by: Rasmus Munk Larsen <rmlarsen@google.com>
---
 src/stt/src/flt/flute.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/stt/src/flt/flute.cpp b/src/stt/src/flt/flute.cpp
index b13efb7b8de..759980fa213 100644
--- a/src/stt/src/flt/flute.cpp
+++ b/src/stt/src/flt/flute.cpp
@@ -319,10 +319,10 @@ static void initLUT(int to_d, LUT_TYPE LUT, NUMSOLN_TYPE numsoln)
     }
     ++pwv;
 #if FLUTE_ROUTING == 1
-    if (pwv[0] == 'd' && pwv[1] == '=') {
-      pwv = readDecimalInt(pwv + 2, d);
+    if (prt[0] == 'd' && prt[1] == '=') {
+      prt = readDecimalInt(prt + 2, d);
     }
-    ++pwv;
+    ++prt;
 #endif
     for (int k = 0; k < numgrp[d]; k++) {
       int ns = charNum(*pwv++);

From 7f0134291710316b1c3978249a650c95b7058965 Mon Sep 17 00:00:00 2001
From: Rasmus Munk Larsen <rmlarsen@google.com>
Date: Thu, 14 Dec 2023 16:21:49 -0800
Subject: [PATCH 4/4] Delete misleading comment.

Signed-off-by: Rasmus Munk Larsen <rmlarsen@google.com>
---
 src/stt/src/flt/flute.cpp | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/stt/src/flt/flute.cpp b/src/stt/src/flt/flute.cpp
index 759980fa213..6843a3eefec 100644
--- a/src/stt/src/flt/flute.cpp
+++ b/src/stt/src/flt/flute.cpp
@@ -281,9 +281,6 @@ static unsigned char charNum(unsigned char c)
   return 0;
 }
 
-// Decodes a decimal integer from the string s.
-// Returns the decoded value in *value and returns
-// the number of characters read.
 inline const char* readDecimalInt(const char* s, int& value)
 {
   value = 0;