From 007f8e32c46370acd1959471ba871f85710f471d Mon Sep 17 00:00:00 2001 From: Nemanja Trifunovic Date: Sat, 6 Apr 2019 12:08:34 -0400 Subject: [PATCH] advance() can work in backward direction. advance() now can decrement the iterator if the number of steps to advance is negative. --- README.md | 14 ++++++-------- source/utf8/checked.h | 12 ++++++++++-- source/utf8/unchecked.h | 12 ++++++++++-- test_drivers/smoke_test/test.cpp | 28 ++++++++++++++++++++++------ 4 files changed, 48 insertions(+), 18 deletions(-) diff --git a/README.md b/README.md index c1bd92f..67d610e 100644 --- a/README.md +++ b/README.md @@ -321,8 +321,8 @@ void advance (octet_iterator& it, distance_type n, octet_iterator end); `octet_iterator`: an input iterator. `distance_type`: an integral type convertible to `octet_iterator`'s difference type. `it`: a reference to an iterator pointing to the beginning of an UTF-8 encoded code point. After the function returns, it is incremented to point to the nth following code point. -`n`: a positive integer that shows how many code points we want to advance. -`end`: end of the UTF-8 sequence to be processed. If `it` gets equal to `end` during the extraction of a code point, an `utf8::not_enough_room` exception is thrown. +`n`: number of code points `it` should be advanced. A negative value means decrement. +`end`: limit of the UTF-8 sequence to be processed. If `n` is positive and `it` gets equal to `end` during the extraction of a code point, an `utf8::not_enough_room` exception is thrown. If `n` is negative and `it` reaches `end` while `it` points t a trail byte of a UTF-8 sequence, a `utf8::invalid_code_point` exception is thrown. Example of use: @@ -331,10 +331,10 @@ char* twochars = "\xe6\x97\xa5\xd1\x88"; unsigned char* w = twochars; advance (w, 2, twochars + 6); assert (w == twochars + 5); +advance (w, -2, twochars); +assert (w == twochars); ``` -This function works only "forward". In case of a negative `n`, there is no effect. - In case of an invalid code point, a `utf8::invalid_code_point` exception is thrown. #### utf8::distance @@ -1049,8 +1049,8 @@ template void advance (octet_iterator& it, distance_type n); ``` -`it`: a reference to an iterator pointing to the beginning of an UTF-8 encoded code point. After the function returns, it is incremented to point to the nth following code point. -`n`: a positive integer that shows how many code points we want to advance. +`it`: a reference to an iterator pointing to the beginning of an UTF-8 encoded code point. After the function returns, it is incremented to point to the nth following code point. +`n`: number of code points `it` should be advanced. A negative value means decrement. Example of use: @@ -1061,8 +1061,6 @@ unchecked::advance (w, 2); assert (w == twochars + 5); ``` -This function works only "forward". In case of a negative `n`, there is no effect. - This is a faster but less safe version of `utf8::advance`. It does not check for validity of the supplied UTF-8 sequence and offers no boundary checking. #### utf8::unchecked::distance diff --git a/source/utf8/checked.h b/source/utf8/checked.h index bba4995..8228b2e 100644 --- a/source/utf8/checked.h +++ b/source/utf8/checked.h @@ -177,8 +177,16 @@ namespace utf8 template void advance (octet_iterator& it, distance_type n, octet_iterator end) { - for (distance_type i = 0; i < n; ++i) - utf8::next(it, end); + const distance_type zero(0); + if (n < zero) { + // backward + for (distance_type i = n; i < zero; ++i) + utf8::prior(it, end); + } else { + // forward + for (distance_type i = zero; i < n; ++i) + utf8::next(it, end); + } } template diff --git a/source/utf8/unchecked.h b/source/utf8/unchecked.h index 3af7c15..c78419f 100644 --- a/source/utf8/unchecked.h +++ b/source/utf8/unchecked.h @@ -105,8 +105,16 @@ namespace utf8 template void advance (octet_iterator& it, distance_type n) { - for (distance_type i = 0; i < n; ++i) - utf8::unchecked::next(it); + const distance_type zero(0); + if (n < zero) { + // backward + for (distance_type i = n; i < zero; ++i) + utf8::unchecked::prior(it); + } else { + // forward + for (distance_type i = zero; i < n; ++i) + utf8::unchecked::next(it); + } } template diff --git a/test_drivers/smoke_test/test.cpp b/test_drivers/smoke_test/test.cpp index ce0480b..42f4cc8 100644 --- a/test_drivers/smoke_test/test.cpp +++ b/test_drivers/smoke_test/test.cpp @@ -66,9 +66,17 @@ int main() assert (w == threechars); // advance - w = twochars; - advance (w, 2, twochars + 6); - assert (w == twochars + 5); + w = threechars; + advance(w, 2, threechars + 9); + assert(w == threechars + 7); + advance(w, -2, threechars); + assert(w == threechars); + advance(w, 3, threechars + 9); + assert(w == threechars + 9); + advance(w, -2, threechars); + assert(w == threechars + 4); + advance(w, -1, threechars); + assert(w == threechars); // distance size_t dist = utf8::distance(twochars, twochars + 5); @@ -194,9 +202,17 @@ int main() assert (cw == twochars); // advance - w = twochars; - unchecked::advance (w, 2); - assert (w == twochars + 5); + w = threechars; + unchecked::advance(w, 2); + assert(w == threechars + 7); + unchecked::advance(w, -2); + assert(w == threechars); + unchecked::advance(w, 3); + assert(w == threechars + 9); + unchecked::advance(w, -2); + assert(w == threechars + 4); + unchecked::advance(w, -1); + assert(w == threechars); // distance dist = unchecked::distance(twochars, twochars + 5);