StdLib/LibC/Containers/Common/ModuloUtil.c

   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
  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
  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
  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
 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
 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 }