merge.go

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package cmerge
     6  
     7  // package cmerge provides a few small utility APIs for helping
     8  // with merging of counter data for a given function.
     9  
    10  import (
    11  	"fmt"
    12  	"internal/coverage"
    13  	"math"
    14  )
    15  
    16  type ModeMergePolicy uint8
    17  
    18  const (
    19  	ModeMergeStrict ModeMergePolicy = iota
    20  	ModeMergeRelaxed
    21  )
    22  
    23  // Merger provides state and methods to help manage the process of
    24  // merging together coverage counter data for a given function, for
    25  // tools that need to implicitly merge counter as they read multiple
    26  // coverage counter data files.
    27  type Merger struct {
    28  	cmode    coverage.CounterMode
    29  	cgran    coverage.CounterGranularity
    30  	policy   ModeMergePolicy
    31  	overflow bool
    32  }
    33  
    34  func (cm *Merger) SetModeMergePolicy(policy ModeMergePolicy) {
    35  	cm.policy = policy
    36  }
    37  
    38  // MergeCounters takes the counter values in 'src' and merges them
    39  // into 'dst' according to the correct counter mode.
    40  func (m *Merger) MergeCounters(dst, src []uint32) (error, bool) {
    41  	if len(src) != len(dst) {
    42  		return fmt.Errorf("merging counters: len(dst)=%d len(src)=%d", len(dst), len(src)), false
    43  	}
    44  	if m.cmode == coverage.CtrModeSet {
    45  		for i := 0; i < len(src); i++ {
    46  			if src[i] != 0 {
    47  				dst[i] = 1
    48  			}
    49  		}
    50  	} else {
    51  		for i := 0; i < len(src); i++ {
    52  			dst[i] = m.SaturatingAdd(dst[i], src[i])
    53  		}
    54  	}
    55  	ovf := m.overflow
    56  	m.overflow = false
    57  	return nil, ovf
    58  }
    59  
    60  // Saturating add does a saturating addition of 'dst' and 'src',
    61  // returning added value or math.MaxUint32 if there is an overflow.
    62  // Overflows are recorded in case the client needs to track them.
    63  func (m *Merger) SaturatingAdd(dst, src uint32) uint32 {
    64  	result, overflow := SaturatingAdd(dst, src)
    65  	if overflow {
    66  		m.overflow = true
    67  	}
    68  	return result
    69  }
    70  
    71  // Saturating add does a saturating addition of 'dst' and 'src',
    72  // returning added value or math.MaxUint32 plus an overflow flag.
    73  func SaturatingAdd(dst, src uint32) (uint32, bool) {
    74  	d, s := uint64(dst), uint64(src)
    75  	sum := d + s
    76  	overflow := false
    77  	if uint64(uint32(sum)) != sum {
    78  		overflow = true
    79  		sum = math.MaxUint32
    80  	}
    81  	return uint32(sum), overflow
    82  }
    83  
    84  // SetModeAndGranularity records the counter mode and granularity for
    85  // the current merge. In the specific case of merging across coverage
    86  // data files from different binaries, where we're combining data from
    87  // more than one meta-data file, we need to check for and resolve
    88  // mode/granularity clashes.
    89  func (cm *Merger) SetModeAndGranularity(mdf string, cmode coverage.CounterMode, cgran coverage.CounterGranularity) error {
    90  	if cm.cmode == coverage.CtrModeInvalid {
    91  		// Set merger mode based on what we're seeing here.
    92  		cm.cmode = cmode
    93  		cm.cgran = cgran
    94  	} else {
    95  		// Granularity clashes are always errors.
    96  		if cm.cgran != cgran {
    97  			return fmt.Errorf("counter granularity clash while reading meta-data file %s: previous file had %s, new file has %s", mdf, cm.cgran.String(), cgran.String())
    98  		}
    99  		// Mode clashes are treated as errors if we're using the
   100  		// default strict policy.
   101  		if cm.cmode != cmode {
   102  			if cm.policy == ModeMergeStrict {
   103  				return fmt.Errorf("counter mode clash while reading meta-data file %s: previous file had %s, new file has %s", mdf, cm.cmode.String(), cmode.String())
   104  			}
   105  			// In the case of a relaxed mode merge policy, upgrade
   106  			// mode if needed.
   107  			if cm.cmode < cmode {
   108  				cm.cmode = cmode
   109  			}
   110  		}
   111  	}
   112  	return nil
   113  }
   114  
   115  func (cm *Merger) ResetModeAndGranularity() {
   116  	cm.cmode = coverage.CtrModeInvalid
   117  	cm.cgran = coverage.CtrGranularityInvalid
   118  	cm.overflow = false
   119  }
   120  
   121  func (cm *Merger) Mode() coverage.CounterMode {
   122  	return cm.cmode
   123  }
   124  
   125  func (cm *Merger) Granularity() coverage.CounterGranularity {
   126  	return cm.cgran
   127  }
   128
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