Move Content to Constants

2019-06-14 22:55:06 -07:00
parent 4330741c5d
commit 45682f0e76
6 changed files with 58 additions and 53 deletions
@@ -28,3 +28,46 @@ export const NULL_CELL_CODE = 0;
 export const WHITESPACE_CELL_CHAR = ' ';
 export const WHITESPACE_CELL_WIDTH = 1;
 export const WHITESPACE_CELL_CODE = 32;
+
+/**
+ * Bitmasks for accessing data in `content`.
+ */
+export const enum Content {
+  /**
+   * bit 1..21    codepoint, max allowed in UTF32 is 0x10FFFF (21 bits taken)
+   *              read:   `codepoint = content & Content.codepointMask;`
+   *              write:  `content |= codepoint & Content.codepointMask;`
+   *                      shortcut if precondition `codepoint <= 0x10FFFF` is met:
+   *                      `content |= codepoint;`
+   */
+  CODEPOINT_MASK = 0x1FFFFF,
+
+  /**
+   * bit 22       flag indication whether a cell contains combined content
+   *              read:   `isCombined = content & Content.isCombined;`
+   *              set:    `content |= Content.isCombined;`
+   *              clear:  `content &= ~Content.isCombined;`
+   */
+  IS_COMBINED_MASK = 0x200000,  // 1 << 21
+
+  /**
+   * bit 1..22    mask to check whether a cell contains any string data
+   *              we need to check for codepoint and isCombined bits to see
+   *              whether a cell contains anything
+   *              read:   `isEmpty = !(content & Content.hasContent)`
+   */
+  HAS_CONTENT_MASK = 0x3FFFFF,
+
+  /**
+   * bit 23..24   wcwidth value of cell, takes 2 bits (ranges from 0..2)
+   *              read:   `width = (content & Content.widthMask) >> Content.widthShift;`
+   *                      `hasWidth = content & Content.widthMask;`
+   *                      as long as wcwidth is highest value in `content`:
+   *                      `width = content >> Content.widthShift;`
+   *              write:  `content |= (width << Content.widthShift) & Content.widthMask;`
+   *                      shortcut if precondition `0 <= width <= 3` is met:
+   *                      `content |= width << Content.widthShift;`
+   */
+  WIDTH_MASK = 0xC00000,   // 3 << 22
+  WIDTH_SHIFT = 22
+}