Modest performance, address #12647

doc/source/whatsnew/v0.18.1.txt

@@ -248,7 +248,7 @@ Deprecations
 Performance Improvements
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
-
+- Improved speed of SAS reader (:issue:`12656`)
 
 - Improved performance of ``DataFrame.to_sql`` when checking case sensitivity for tables. Now only checks if table has been created correctly when table name is not lower case. (:issue:`12876`)
 
@@ -281,6 +281,7 @@ Bug Fixes
 - Bug in ``.drop()`` with a non-unique ``MultiIndex``. (:issue:`12701`)
 - Bug in ``.concat`` of datetime tz-aware and naive DataFrames (:issue:`12467`)
 - Bug in correctly raising a ``ValueError`` in ``.resample(..).fillna(..)`` when passing a non-string (:issue:`12952`)
+- Various encoding and header processing issues in SAS reader (:issue:`12659`, :issue:`12654`, :issue:`12647`, :issue:`12809`, :issue:`12656`)
 
 - Bug in ``Timestamp.__repr__`` that caused ``pprint`` to fail in nested structures (:issue:`12622`)
 - Bug in ``Timedelta.min`` and ``Timedelta.max``, the properties now report the true minimum/maximum ``timedeltas`` as recognized by Pandas. See :ref:`documentation <timedeltas.limitations>`. (:issue:`12727`)

pandas/io/sas/sas_constants.py

@@ -0,0 +1,147 @@
+magic = (b"\x00\x00\x00\x00\x00\x00\x00\x00" +
+         b"\x00\x00\x00\x00\xc2\xea\x81\x60" +
+         b"\xb3\x14\x11\xcf\xbd\x92\x08\x00" +
+         b"\x09\xc7\x31\x8c\x18\x1f\x10\x11")
+
+align_1_checker_value = b'3'
+align_1_offset = 32
+align_1_length = 1
+align_1_value = 4
+u64_byte_checker_value = b'3'
+align_2_offset = 35
+align_2_length = 1
+align_2_value = 4
+endianness_offset = 37
+endianness_length = 1
+platform_offset = 39
+platform_length = 1
+encoding_offset = 70
+encoding_length = 1
+dataset_offset = 92
+dataset_length = 64
+file_type_offset = 156
+file_type_length = 8
+date_created_offset = 164
+date_created_length = 8
+date_modified_offset = 172
+date_modified_length = 8
+header_size_offset = 196
+header_size_length = 4
+page_size_offset = 200
+page_size_length = 4
+page_count_offset = 204
+page_count_length = 4
+sas_release_offset = 216
+sas_release_length = 8
+sas_server_type_offset = 224
+sas_server_type_length = 16
+os_version_number_offset = 240
+os_version_number_length = 16
+os_maker_offset = 256
+os_maker_length = 16
+os_name_offset = 272
+os_name_length = 16
+page_bit_offset_x86 = 16
+page_bit_offset_x64 = 32
+subheader_pointer_length_x86 = 12
+subheader_pointer_length_x64 = 24
+page_type_offset = 0
+page_type_length = 2
+block_count_offset = 2
+block_count_length = 2
+subheader_count_offset = 4
+subheader_count_length = 2
+page_meta_type = 0
+page_data_type = 256
+page_amd_type = 1024
+page_metc_type = 16384
+page_comp_type = -28672
+page_mix_types = [512, 640]
+subheader_pointers_offset = 8
+truncated_subheader_id = 1
+compressed_subheader_id = 4
+compressed_subheader_type = 1
+text_block_size_length = 2
+row_length_offset_multiplier = 5
+row_count_offset_multiplier = 6
+col_count_p1_multiplier = 9
+col_count_p2_multiplier = 10
+row_count_on_mix_page_offset_multiplier = 15
+column_name_pointer_length = 8
+column_name_text_subheader_offset = 0
+column_name_text_subheader_length = 2
+column_name_offset_offset = 2
+column_name_offset_length = 2
+column_name_length_offset = 4
+column_name_length_length = 2
+column_data_offset_offset = 8
+column_data_length_offset = 8
+column_data_length_length = 4
+column_type_offset = 14
+column_type_length = 1
+column_format_text_subheader_index_offset = 22
+column_format_text_subheader_index_length = 2
+column_format_offset_offset = 24
+column_format_offset_length = 2
+column_format_length_offset = 26
+column_format_length_length = 2
+column_label_text_subheader_index_offset = 28
+column_label_text_subheader_index_length = 2
+column_label_offset_offset = 30
+column_label_offset_length = 2
+column_label_length_offset = 32
+column_label_length_length = 2
+rle_compression = b'SASYZCRL'
+rdc_compression = b'SASYZCR2'
+
+compression_literals = [rle_compression, rdc_compression]
+
+# Incomplete list of encodings, using SAS nomenclature:
+# http://support.sas.com/documentation/cdl/en/nlsref/61893/HTML/default/viewer.htm#a002607278.htm
+encoding_names = {29: "latin1", 20: "utf-8", 33: "cyrillic", 60: "wlatin2",
+                  61: "wcyrillic", 62: "wlatin1", 90: "ebcdic870"}
+
+
+class index:
+    rowSizeIndex = 0
+    columnSizeIndex = 1
+    subheaderCountsIndex = 2
+    columnTextIndex = 3
+    columnNameIndex = 4
+    columnAttributesIndex = 5
+    formatAndLabelIndex = 6
+    columnListIndex = 7
+    dataSubheaderIndex = 8
+
+
+subheader_signature_to_index = {
+    b"\xF7\xF7\xF7\xF7": index.rowSizeIndex,
+    b"\x00\x00\x00\x00\xF7\xF7\xF7\xF7": index.rowSizeIndex,
+    b"\xF7\xF7\xF7\xF7\x00\x00\x00\x00": index.rowSizeIndex,
+    b"\xF7\xF7\xF7\xF7\xFF\xFF\xFB\xFE": index.rowSizeIndex,
+    b"\xF6\xF6\xF6\xF6": index.columnSizeIndex,
+    b"\x00\x00\x00\x00\xF6\xF6\xF6\xF6": index.columnSizeIndex,
+    b"\xF6\xF6\xF6\xF6\x00\x00\x00\x00": index.columnSizeIndex,
+    b"\xF6\xF6\xF6\xF6\xFF\xFF\xFB\xFE": index.columnSizeIndex,
+    b"\x00\xFC\xFF\xFF": index.subheaderCountsIndex,
+    b"\xFF\xFF\xFC\x00": index.subheaderCountsIndex,
+    b"\x00\xFC\xFF\xFF\xFF\xFF\xFF\xFF": index.subheaderCountsIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFC\x00": index.subheaderCountsIndex,
+    b"\xFD\xFF\xFF\xFF": index.columnTextIndex,
+    b"\xFF\xFF\xFF\xFD": index.columnTextIndex,
+    b"\xFD\xFF\xFF\xFF\xFF\xFF\xFF\xFF": index.columnTextIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFD": index.columnTextIndex,
+    b"\xFF\xFF\xFF\xFF": index.columnNameIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF": index.columnNameIndex,
+    b"\xFC\xFF\xFF\xFF": index.columnAttributesIndex,
+    b"\xFF\xFF\xFF\xFC": index.columnAttributesIndex,
+    b"\xFC\xFF\xFF\xFF\xFF\xFF\xFF\xFF": index.columnAttributesIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFC": index.columnAttributesIndex,
+    b"\xFE\xFB\xFF\xFF": index.formatAndLabelIndex,
+    b"\xFF\xFF\xFB\xFE": index.formatAndLabelIndex,
+    b"\xFE\xFB\xFF\xFF\xFF\xFF\xFF\xFF": index.formatAndLabelIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFB\xFE": index.formatAndLabelIndex,
+    b"\xFE\xFF\xFF\xFF": index.columnListIndex,
+    b"\xFF\xFF\xFF\xFE": index.columnListIndex,
+    b"\xFE\xFF\xFF\xFF\xFF\xFF\xFF\xFF": index.columnListIndex,
+    b"\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFE": index.columnListIndex}