[libc] Templatize the scanf Reader interface (llvm#131037)

This allows specializing the implementation for different targets
without including unnecessary logic and is similar to llvm#111559 which did
the same for printf Writer interface.

Author: petrhosek

libc/src/stdio/CMakeLists.txt

@@ -117,8 +117,8 @@ add_entrypoint_object(
     sscanf.h
   DEPENDS
     libc.src.__support.arg_list
-    libc.src.stdio.scanf_core.reader
     libc.src.stdio.scanf_core.scanf_main
+    libc.src.stdio.scanf_core.string_reader
 )
 
 add_entrypoint_object(
@@ -129,8 +129,8 @@ add_entrypoint_object(
     vsscanf.h
   DEPENDS
     libc.src.__support.arg_list
-    libc.src.stdio.scanf_core.reader
     libc.src.stdio.scanf_core.scanf_main
+    libc.src.stdio.scanf_core.string_reader
 )
 
 add_entrypoint_object(

libc/src/stdio/scanf_core/CMakeLists.txt

@@ -61,10 +61,8 @@ if(NOT(TARGET libc.src.__support.File.file) AND LLVM_LIBC_FULL_BUILD AND
   return()
 endif()
 
-add_object_library(
+add_header_library(
   scanf_main
-  SRCS
-    scanf_main.cpp
   HDRS
     scanf_main.h
   DEPENDS
@@ -83,18 +81,19 @@ add_header_library(
     reader.h
   DEPENDS
     libc.src.__support.macros.attributes
-    ${file_deps}
-  ${use_system_file}
 )
 
-add_object_library(
+add_header_library(
+  string_reader
+  HDRS
+    string_reader.h
+  DEPENDS
+    .reader
+    libc.src.__support.macros.attributes
+)
+
+add_header_library(
   converter
-  SRCS
-    converter.cpp
-    string_converter.cpp
-    int_converter.cpp
-    float_converter.cpp
-    ptr_converter.cpp
   HDRS
     converter.h
     converter_utils.h

libc/src/stdio/scanf_core/converter.cpp

@@ -10,10 +10,19 @@
 #define LLVM_LIBC_SRC_STDIO_SCANF_CORE_CONVERTER_H
 
 #include "src/__support/CPP/string_view.h"
+#include "src/__support/ctype_utils.h"
 #include "src/__support/macros/config.h"
 #include "src/stdio/scanf_core/core_structs.h"
 #include "src/stdio/scanf_core/reader.h"
 
+#ifndef LIBC_COPT_SCANF_DISABLE_FLOAT
+#include "src/stdio/scanf_core/float_converter.h"
+#endif // LIBC_COPT_SCANF_DISABLE_FLOAT
+#include "src/stdio/scanf_core/current_pos_converter.h"
+#include "src/stdio/scanf_core/int_converter.h"
+#include "src/stdio/scanf_core/ptr_converter.h"
+#include "src/stdio/scanf_core/string_converter.h"
+
 #include <stddef.h>
 
 namespace LIBC_NAMESPACE_DECL {
@@ -22,11 +31,81 @@ namespace scanf_core {
 // convert will call a conversion function to convert the FormatSection into
 // its string representation, and then that will write the result to the
 // reader.
-int convert(Reader *reader, const FormatSection &to_conv);
+template <typename T>
+int convert(Reader<T> *reader, const FormatSection &to_conv) {
+  int ret_val = 0;
+  switch (to_conv.conv_name) {
+  case '%':
+    return raw_match(reader, "%");
+  case 's':
+    ret_val = raw_match(reader, " ");
+    if (ret_val != READ_OK)
+      return ret_val;
+    return convert_string(reader, to_conv);
+  case 'c':
+  case '[':
+    return convert_string(reader, to_conv);
+  case 'd':
+  case 'i':
+  case 'u':
+  case 'o':
+  case 'x':
+  case 'X':
+    ret_val = raw_match(reader, " ");
+    if (ret_val != READ_OK)
+      return ret_val;
+    return convert_int(reader, to_conv);
+#ifndef LIBC_COPT_SCANF_DISABLE_FLOAT
+  case 'f':
+  case 'F':
+  case 'e':
+  case 'E':
+  case 'a':
+  case 'A':
+  case 'g':
+  case 'G':
+    ret_val = raw_match(reader, " ");
+    if (ret_val != READ_OK)
+      return ret_val;
+    return convert_float(reader, to_conv);
+#endif // LIBC_COPT_SCANF_DISABLE_FLOAT
+  case 'n':
+    return convert_current_pos(reader, to_conv);
+  case 'p':
+    ret_val = raw_match(reader, " ");
+    if (ret_val != READ_OK)
+      return ret_val;
+    return convert_pointer(reader, to_conv);
+  default:
+    return raw_match(reader, to_conv.raw_string);
+  }
+  return -1;
+}
 
 // raw_match takes a raw string and matches it to the characters obtained from
 // the reader.
-int raw_match(Reader *reader, cpp::string_view raw_string);
+template <typename T>
+int raw_match(Reader<T> *reader, cpp::string_view raw_string) {
+  char cur_char = reader->getc();
+  int ret_val = READ_OK;
+  for (size_t i = 0; i < raw_string.size(); ++i) {
+    // Any space character matches any number of space characters.
+    if (internal::isspace(raw_string[i])) {
+      while (internal::isspace(cur_char)) {
+        cur_char = reader->getc();
+      }
+    } else {
+      if (raw_string[i] == cur_char) {
+        cur_char = reader->getc();
+      } else {
+        ret_val = MATCHING_FAILURE;
+        break;
+      }
+    }
+  }
+  reader->ungetc(cur_char);
+  return ret_val;
+}
 
 } // namespace scanf_core
 } // namespace LIBC_NAMESPACE_DECL

libc/src/stdio/scanf_core/converter.h

@@ -19,7 +19,8 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace scanf_core {
 
-LIBC_INLINE int convert_current_pos(Reader *reader,
+template <typename T>
+LIBC_INLINE int convert_current_pos(Reader<T> *reader,
                                     const FormatSection &to_conv) {
   write_int_with_length(reader->chars_read(), to_conv);
   return READ_OK;