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authorRoberto Ierusalimschy <roberto@inf.puc-rio.br>2023-11-24 14:41:07 -0300
committerRoberto Ierusalimschy <roberto@inf.puc-rio.br>2023-11-24 14:41:07 -0300
commit52b899d60d8c61b8affe0206014173912de94940 (patch)
tree5e6f9116b2c70a5ebd4c1bdea49f283cca5cb3fb /ltable.h
parent25cd3d377ec13176a6701d9d21a278ba8f2bc3d6 (diff)
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Simpler coding for new representation for arrays
With the tags comming first in a cell, we can define the whole cell as a C type and let C do part of the address computations.
Diffstat (limited to 'ltable.h')
-rw-r--r--ltable.h38
1 files changed, 8 insertions, 30 deletions
diff --git a/ltable.h b/ltable.h
index d488a1f7..5581efb1 100644
--- a/ltable.h
+++ b/ltable.h
@@ -69,44 +69,22 @@
69 69
70/* 70/*
71** The array part of a table is represented by an array of cells. 71** The array part of a table is represented by an array of cells.
72** Each cell is composed of (NM + 1) elements, and each element has the 72** Each cell is composed of NM tags followed by NM values, so that
73** type 'ArrayCell'. In each cell, only one element has the variant 73** no space is wasted in padding.
74** 'tag', while the other NM elements have the variant 'value'. The
75** array in the 'tag' element holds the tags of the other elements in
76** that cell.
77*/ 74*/
78#define NM ((unsigned int)sizeof(Value)) 75#define NM cast_uint(sizeof(Value))
79 76
80union ArrayCell { 77struct ArrayCell {
81 unsigned char tag[NM]; 78 lu_byte tag[NM];
82 Value value; 79 Value value[NM];
83}; 80};
84 81
85 82
86/*
87** 'NMTag' defines which cell element has the tags; that could be any
88** value between 0 (tags come before all values) and NM (tags come after
89** all values).
90*/
91#define NMTag 0
92
93
94/*
95** Computes the concrete index that holds the tag of abstract index 'i'
96*/
97#define TagIndex(i) (((i)/NM * (NM + 1u)) + NMTag)
98
99/*
100** Computes the concrete index that holds the value of abstract index 'i'
101*/
102#define ValueIndex(i) ((i) + (((i) + (NM - NMTag))/NM))
103
104
105/* Computes the address of the tag for the abstract index 'k' */ 83/* Computes the address of the tag for the abstract index 'k' */
106#define getArrTag(t,k) (&(t)->array[TagIndex(k)].tag[(k)%NM]) 84#define getArrTag(t,k) (&(t)->array[(k)/NM].tag[(k)%NM])
107 85
108/* Computes the address of the value for the abstract index 'k' */ 86/* Computes the address of the value for the abstract index 'k' */
109#define getArrVal(t,k) (&(t)->array[ValueIndex(k)].value) 87#define getArrVal(t,k) (&(t)->array[(k)/NM].value[(k)%NM])
110 88
111 89
112/* 90/*