Implement grapheme seg algo in Go

tools/wcswidth/char-props-data.go

@@ -86,6 +86,10 @@ func (s *CharProps) Set_shifted_width(val uint8) {
 	*s |= CharProps(val&0b111) << 7
 }
 
+func (s CharProps) Width() int {
+	return int(s.Shifted_width()) - 4
+}
+
 const charprops_mask = 127
 const charprops_shift = 7
 

tools/wcswidth/char-props.go

@@ -0,0 +1,101 @@
+package wcswidth
+
+import (
+	"fmt"
+)
+
+var _ = fmt.Print
+
+type GraphemeSegmentationState struct {
+	last_char_prop GraphemeBreakProperty
+
+	/* True if the last character ends a sequence of Indic_Conjunct_Break
+	values:  consonant {extend|linker}*  */
+	incb_consonant_extended bool
+	/* True if the last character ends a sequence of Indic_Conjunct_Break
+	values:  consonant {extend|linker}* linker  */
+	incb_consonant_extended_linker bool
+	/* True if the last character ends a sequence of Indic_Conjunct_Break
+	values:  consonant {extend|linker}* linker {extend|linker}*  */
+	incb_consonant_extended_linker_extended bool
+
+	/* True if the last character ends an emoji modifier sequence
+	   \p{Extended_Pictographic} Extend*.  */
+	emoji_modifier_sequence bool
+	/* True if the last character was immediately preceded by an
+	   emoji modifier sequence   \p{Extended_Pictographic} Extend*.  */
+	emoji_modifier_sequence_before_last_char bool
+
+	/* Number of consecutive regional indicator (RI) characters seen
+	   immediately before the current point.  */
+	ri_count uint
+}
+
+func Char_props_for(ch rune) CharProps {
+	return charprops_t2[(rune(charprops_t1[ch>>charprops_shift])<<charprops_shift)+(ch&charprops_mask)]
+}
+
+func (i IndicConjunctBreak) is_linker_or_extend() bool {
+	return i == ICB_Linker || i == ICB_Extend
+}
+
+func (s *GraphemeSegmentationState) Step(ch CharProps) bool {
+	// Grapheme segmentation as per UAX29-C1-1 as defined in https://www.unicode.org/reports/tr29/
+	// Returns true iff ch should be added to the current cell based on s which
+	// must reflect the state of the current cell. s is updated by ch.
+	prop := GraphemeBreakProperty(ch.Grapheme_break())
+	incb := IndicConjunctBreak(ch.Indic_conjunct_break())
+	add_to_cell := false
+	if s.last_char_prop == GBP_AtStart {
+		add_to_cell = true
+	} else {
+		/* No break between CR and LF (GB3).  */
+		if s.last_char_prop == GBP_CR && prop == GBP_LF {
+			add_to_cell = true
+		} else if
+		/* Break before and after newlines (GB4, GB5).  */
+		(s.last_char_prop == GBP_CR || s.last_char_prop == GBP_LF || s.last_char_prop == GBP_Control) ||
+			(prop == GBP_CR || prop == GBP_LF || prop == GBP_Control) {
+		} else if
+		/* No break between Hangul syllable sequences (GB6, GB7, GB8).  */
+		(s.last_char_prop == GBP_L && (prop == GBP_L || prop == GBP_V || prop == GBP_LV || prop == GBP_LVT)) ||
+			((s.last_char_prop == GBP_LV || s.last_char_prop == GBP_V) && (prop == GBP_V || prop == GBP_T)) ||
+			((s.last_char_prop == GBP_LVT || s.last_char_prop == GBP_T) && prop == GBP_T) {
+			add_to_cell = true
+		} else if
+		/* No break before: extending characters or ZWJ (GB9), SpacingMarks (GB9a), Prepend characters (GB9b)  */
+		prop == GBP_Extend || prop == GBP_ZWJ || prop == GBP_SpacingMark || s.last_char_prop == GBP_Prepend {
+			add_to_cell = true
+		} else if
+		/* No break within certain combinations of Indic_Conjunct_Break values:
+		 * Between consonant {extend|linker}* linker {extend|linker}* and consonant (GB9c).  */
+		s.incb_consonant_extended_linker_extended && incb == ICB_Consonant {
+			add_to_cell = true
+		} else if
+		/* No break within emoji modifier sequences or emoji zwj sequences (GB11).  */
+		s.last_char_prop == GBP_ZWJ && s.emoji_modifier_sequence_before_last_char && (ch.Is_extended_pictographic() == 1) {
+			add_to_cell = true
+		} else if
+		/* No break between RI if there is an odd number of RI characters before (GB12, GB13).  */
+		prop == GBP_Regional_Indicator && (s.ri_count%2) != 0 {
+			add_to_cell = true
+		} else
+		/* Break everywhere else */
+		{
+		}
+	}
+
+	s.incb_consonant_extended_linker = s.incb_consonant_extended && incb == ICB_Linker
+	s.incb_consonant_extended_linker_extended = (s.incb_consonant_extended_linker || (s.incb_consonant_extended_linker_extended && incb.is_linker_or_extend()))
+	s.incb_consonant_extended = (incb == ICB_Consonant || (s.incb_consonant_extended && incb.is_linker_or_extend()))
+	s.emoji_modifier_sequence_before_last_char = s.emoji_modifier_sequence
+	s.emoji_modifier_sequence = (s.emoji_modifier_sequence && prop == GBP_Extend) || (ch.Is_extended_pictographic() == 1)
+	s.last_char_prop = prop
+
+	if prop == GBP_Regional_Indicator {
+		s.ri_count++
+	} else {
+		s.ri_count = 0
+	}
+	return add_to_cell
+}