1 /** @file
2 Utility functions for performing basic math operations constrained within a
3 modulus.
4
5 These functions are intended to simplify small changes to a value which much
6 remain within a specified modulus.
7
8 NOTE: Changes must be less than or equal to the modulus specified by MaxVal.
9
10 Copyright (c) 2012, Intel Corporation. All rights reserved.<BR>
11 This program and the accompanying materials are licensed and made available
12 under the terms and conditions of the BSD License which accompanies this
13 distribution. The full text of the license may be found at
14 http://opensource.org/licenses/bsd-license.php.
15
16 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
17 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
18 **/
19 #include <Uefi.h>
20 #include <LibConfig.h>
21 #include <assert.h>
22
23 /** Counter = (Counter + 1) % MaxVal;
24
25 Counter is always expected to be LESS THAN MaxVal.
26 0 <= Counter < MaxVal
27
28 @param[in] Counter The value to be incremented.
29 @param[in] MaxVal Modulus of the operation.
30
31 @return Returns the result of incrementing Counter, modulus MaxVal.
32 If Counter >= MaxVal, returns -1.
33 **/
34 INT32
35 EFIAPI
ModuloIncrement(UINT32 Counter,UINT32 MaxVal)36 ModuloIncrement(
37 UINT32 Counter,
38 UINT32 MaxVal
39 )
40 {
41 INT32 Temp;
42
43 if(Counter < MaxVal) {
44 Temp = (INT32)(Counter + 1);
45 if(Temp >= (INT32)MaxVal) {
46 Temp = 0;
47 }
48 }
49 else {
50 Temp = -1;
51 }
52 return Temp;
53 }
54
55 /** Counter = (Counter - 1) % MaxVal;
56
57 Counter is always expected to be LESS THAN MaxVal.
58 0 <= Counter < MaxVal
59
60 @param[in] Counter The value to be decremented.
61 @param[in] MaxVal Modulus of the operation.
62
63 @return Returns the result of decrementing Counter, modulus MaxVal.
64 If Counter >= MaxVal, returns -1.
65 **/
66 INT32
67 EFIAPI
ModuloDecrement(UINT32 Counter,UINT32 MaxVal)68 ModuloDecrement(
69 UINT32 Counter,
70 UINT32 MaxVal
71 )
72 {
73 INT32 Temp;
74
75 if(Counter < MaxVal) {
76 Temp = (INT32)Counter - 1;
77 // If Counter is zero, Temp will become -1.
78 if(Temp < 0) {
79 Temp = (INT32)MaxVal - 1;
80 }
81 }
82 else {
83 Temp = -1;
84 }
85
86 return Temp;
87 }
88
89 /** Decrement Counter but don't decrement past zero.
90
91 @param[in] Counter The value to be decremented.
92
93 @return Returns the result of decrementing Counter.
94 **/
95 UINT32
96 EFIAPI
BoundDecrement(UINT32 Counter)97 BoundDecrement(
98 UINT32 Counter
99 )
100 {
101 return ((Counter > 0) ? (Counter - 1) : 0);
102 }
103
104 /** Increment Counter but don't increment past MaxVal.
105 Counter should be maintained in the range (0 <= Counter < MaxVal).
106
107 @param[in] Counter The value to be decremented.
108 @param[in] MaxVal The upper bound for Counter.
109
110 @return Returns the result of incrementing Counter.
111 **/
112 UINT32
113 EFIAPI
BoundIncrement(UINT32 Counter,UINT32 MaxVal)114 BoundIncrement(
115 UINT32 Counter,
116 UINT32 MaxVal
117 )
118 {
119 return ((Counter < (MaxVal - 1)) ? (Counter + 1) : (MaxVal - 1));
120 }
121
122 /** Counter = (Counter + Increment) % MaxVal;
123
124 @param[in] Counter The value to be incremented.
125 @param[in] Increment The value to add to Counter.
126 @param[in] MaxVal Modulus of the operation.
127
128 @return Returns the result of adding Increment to Counter, modulus MaxVal,
129 or -1 if Increment is larger than MaxVal.
130 **/
131 INT32
132 EFIAPI
ModuloAdd(UINT32 Counter,UINT32 Increment,UINT32 MaxVal)133 ModuloAdd (
134 UINT32 Counter,
135 UINT32 Increment,
136 UINT32 MaxVal
137 )
138 {
139 UINT32 Temp;
140
141 if(Increment > MaxVal) {
142 return -1;
143 }
144 Temp = (Counter + Increment);
145 while(Temp >= MaxVal) {
146 Temp -= MaxVal;
147 }
148 return Temp;
149 }
150