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Reactos
1/***
2*strncmp.c - compare first n characters of two strings
3*
4* Copyright (c) Microsoft Corporation. All rights reserved.
5*
6*Purpose:
7* defines strncmp() - compare first n characters of two strings
8* for ordinal order.
9*
10*******************************************************************************/
11
12#include <string.h>
13
14#ifdef _M_ARM
15 #pragma function(strncmp)
16#endif
17
18/***
19*int strncmp(first, last, count) - compare first count chars of strings
20*
21*Purpose:
22* Compares two strings for ordinal order. The comparison stops
23* after: (1) a difference between the strings is found, (2) the end
24* of the strings is reached, or (3) count characters have been
25* compared.
26*
27*Entry:
28* char *first, *last - strings to compare
29* unsigned count - maximum number of characters to compare
30*
31*Exit:
32* returns <0 if first < last
33* returns 0 if first == last
34* returns >0 if first > last
35*
36*Exceptions:
37*
38*******************************************************************************/
39
40int __cdecl strncmp
41(
42 const char *first,
43 const char *last,
44 size_t count
45)
46{
47 size_t x = 0;
48
49 if (!count)
50 {
51 return 0;
52 }
53
54 /*
55 * This explicit guard needed to deal correctly with boundary
56 * cases: strings shorter than 4 bytes and strings longer than
57 * UINT_MAX-4 bytes .
58 */
59 if( count >= 4 )
60 {
61 /* unroll by four */
62 for (; x < count-4; x+=4)
63 {
64 first+=4;
65 last +=4;
66
67 if (*(first-4) == 0 || *(first-4) != *(last-4))
68 {
69 return(*(unsigned char *)(first-4) - *(unsigned char *)(last-4));
70 }
71
72 if (*(first-3) == 0 || *(first-3) != *(last-3))
73 {
74 return(*(unsigned char *)(first-3) - *(unsigned char *)(last-3));
75 }
76
77 if (*(first-2) == 0 || *(first-2) != *(last-2))
78 {
79 return(*(unsigned char *)(first-2) - *(unsigned char *)(last-2));
80 }
81
82 if (*(first-1) == 0 || *(first-1) != *(last-1))
83 {
84 return(*(unsigned char *)(first-1) - *(unsigned char *)(last-1));
85 }
86 }
87 }
88
89 /* residual loop */
90 for (; x < count; x++)
91 {
92 if (*first == 0 || *first != *last)
93 {
94 return(*(unsigned char *)first - *(unsigned char *)last);
95 }
96 first+=1;
97 last+=1;
98 }
99
100 return 0;
101}