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Sean Barker
C Structs
1
a
r
i next
struct rec { int a[4]; size_t i; struct rec next; };* struct rec x; struct rec y; x.i = 5; x.a[1] = 2; x.next = &y; y = x; // copy full struct struct rec* z; z = &y; // just a pointer copy // form 1 (*z).i = 7; // NOT z.i = 7; // form 2 (preferred) z->i = 7;
typedef
// give type T another name: U typedef T U; // example: defines a type “struct rec” // and typedefs it with another name “rec” typedef struct rec { ... } rec; rec x; // now can omit “struct” x.i = 5; rec* p = (rec*) malloc(sizeof(rec)); p->i = 3;
Sean Barker
Linked List Example
3 .L11: # loop: movslq 16(%rdi), %rax # i = M[r+16] movl %esi, (%rdi,%rax,4) # M[r+4i] = val movq 24(%rdi), %rdi # r = M[r+24] testq %rdi, %rdi # Test r jne .L11 # if !=0 goto loop void set_val (struct rec r, int val) { while (r) { int i = r->i; r->a[i] = val; r = r->next; } } Register Value %rdi r %rsi val struct rec { int a[4]; int i; struct rec* next; }; Element i r i next 0 16 24 32 a**
Data Alignment
*struct S1 { char c; int i[2]; double v; } p;
Unaligned Data
c i[0] i[1] v p p+1 p+5 p+9 p+
Aligned Data
c 3 bytes^ i[0] i[1] 4 bytes v
p+0 p+4 p+8 p+16 p+
Mul3ple of 4 Mul3ple of 8
Mul3ple of 8 Mul3ple of 8
Floating Point: YMM/XMM Registers
n 16 single-byte integers n 8 16-bit integers n 4 32-bit integers n 4 single-precision floats n 2 double-precision floats n 1 single-precision float n 1 double-precision float
