lukaszgryglicki/jpegbw: cmd/jpeg/jpeg.go; 383 LoC

Found a possible issue in [lukaszgryglicki/jpegbw](https://www.github.com/lukaszgryglicki/jpegbw) at [cmd/jpeg/jpeg.go](https://github.com/lukaszgryglicki/jpegbw/blob/1e2480f4449a7db41c44100807e88c25855e97b3/cmd/jpeg/jpeg.go#L630-L1012)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first issue it finds, so please do not limit your consideration to the contents of the below message.

> range-loop variable colidx used in defer or goroutine at line 920

[Click here to see the code in its original context.](https://github.com/lukaszgryglicki/jpegbw/blob/1e2480f4449a7db41c44100807e88c25855e97b3/cmd/jpeg/jpeg.go#L630-L1012)

Click here to show the 383 line(s) of Go which triggered the analyzer.

```go
for colidx, colrgba := range rgba {
if noA && colidx == 3 {
continue
}
r := ar[colidx]
g := ag[colidx]
b := ab[colidx]
lo := alo[colidx]
loi := aloi[colidx]
hi := ahi[colidx]
hii := ahii[colidx]
ga := aga[colidx]
gaB := agaB[colidx]

if useHints && usedHint {
loi = hint.LoIdx[colidx]
hii = hint.HiIdx[colidx]
// info: fmt.Printf("Using hint scale: %04x-%04x\n", loi, hii)
}

hist := make(jpegbw.IntHist)
minGs := uint16(0xffff)
maxGs := uint16(0)

dtStartH := time.Now()
loI := uint16(0)
hiI := uint16(0)
if inf > 0 || loi == 0 || hii == 0xffff {
for i := 0; i < xo; i++ {
for j := 0; j < yo; j++ {
pr, pg, pb, _ := m.At(i, j).RGBA()
// debug2: fmt.Printf("(%d,%d,%d)\n", pr, pg, pb)
gs := uint16(r*float64(pr) + g*float64(pg) + b*float64(pb))
if gs < minGs {
minGs = gs
}
if gs > maxGs {
maxGs = gs
}
hist[gs]++
}
}
// info: fmt.Printf("hist: %+v\n", hist.str())

// Calculations
histCum := make(jpegbw.FloatHist)
sum := int64(0)
for i := uint16(0); true; i++ {
sum += hist[i]
histCum[i] = (float64(sum) * 100.0) / all
if i == 0xffff {
break
}
}
for i := uint16(1); true; i++ {
prev := histCum[i-1]
next := histCum[i]
if loI == 0 && prev <= lo && lo <= next {
loI = i
}
if prev <= hi && hi <= next {
hiI = i
}
if i == 0xffff {
break
}
}
if loi > 0 && loi != loI {
// info: fmt.Printf("Overwriting %s low index: %04x -> %04x\n", colrgba, loI, loi)
loI = loi
}
if hii < 0xffff && hii != hiI {
// info: fmt.Printf("Overwriting %s high index: %04x -> %04x\n", colrgba, hiI, hii)
hiI = hii
}
if loI >= hiI {
return fmt.Errorf("calculated integer range is empty: %d-%d", loI, hiI)
}
} else {
loI = loi
hiI = hii
}
mult := 65535.0 / float64(hiI-loI)
// info: fmt.Printf("histCum: %+v\n", histCum.str())

// In INF mode we need histogramScaled context
if inf > 0 {
b := 65535.0 / float64(x)
histScaled := make(jpegbw.IntHist)
maxHS := int64(0)
if bhpow {
for i := uint16(0); i < uint16(x); i++ {
ff := (float64(i) * b) / 65535.0
f := uint16(math.Pow(ff, shpow) * 65535.0)
tf := (float64(i+1) * b) / 65535.0
t := uint16(math.Pow(tf, shpow) * 65535.0)
if t == f {
t++
}
hv := int64(0)
for h := f; h < t; h++ {
hv += hist[h]
}
histScaled[i] = hv
if hv > maxHS {
maxHS = hv
}
}
} else {
for i := uint16(0); i < uint16(x); i++ {
f := uint16(float64(i) * b)
t := uint16(float64(i+1) * b)
if t == f {
t++
}
hv := int64(0)
for h := f; h < t; h++ {
hv += hist[h]
}
histScaled[i] = hv
if hv > maxHS {
maxHS = hv
}
}
}
fran := float64((hiI - loI) + 1)
b2 := fran / float64(x)
histScaled2 := make(jpegbw.IntHist)
maxHS2 := int64(0)
for i := uint16(0); i < uint16(x); i++ {
f := loI + uint16(float64(i)*b2)
t := uint16(float64(f) + b2)
if t == f {
t++
}
hv := int64(0)
for h := f; h < t; h++ {
hv += hist[h]
}
histScaled2[i] = hv
if hv > maxHS2 {
maxHS2 = hv
}
}
prev := int64(0)
next := int64(0)
prevI := uint16(0xffff)
for i := uint16(0); i < uint16(x); i++ {
v := histScaled[i]
if v > 0 {
prev = v
prevI = i
} else {
nextJ := uint16(0xffff)
for j := i + 1; j < uint16(x); j++ {
w := histScaled[j]
if w > 0 {
next = w
nextJ = j
break
}
}
if prevI != 0xffff && nextJ != 0xffff {
histScaled[i] = prev + int64((float64(i-prevI)/float64(nextJ-prevI))*float64(next-prev))
}
}
}
prev = 0
next = 0
prevI = uint16(0xffff)
for i := uint16(0); i < uint16(x); i++ {
v := histScaled2[i]
if v > 0 {
prev = v
prevI = i
} else {
nextJ := uint16(0xffff)
for j := i + 1; j < uint16(x); j++ {
w := histScaled2[j]
if w > 0 {
next = w
nextJ = j
break
}
}
if prevI != 0xffff && nextJ != 0xffff {
histScaled2[i] = prev + int64((float64(i-prevI)/float64(nextJ-prevI))*float64(next-prev))
}
}
}
maxHSF := float64(maxHS)
maxHSF2 := float64(maxHS2)
finf := float64(inf * 2)
// debug: fmt.Printf("histScaled: %+v\n", histScaled.str())
ran := (hiI - loI) + 1
ran4 := (ran + 1) / 4
if ran == 0 {
ran = 0xffff
}
if ran4 == 0 {
ran4 = 0x4000
}
getPixelFunc = func(img *image.Image, i, j int) (uint32, uint32, uint32, uint32) {
if i < x-inf && j < y-(2*inf) {
// normal pixel
return (*img).At(i, j).RGBA()
} else if j < y-(2*inf) {
// scale on the right: GS or GS, R, G, B
if einf {
g := (uint32(j) * uint32(ran)) / uint32(y-2*inf)
d := g / uint32(ran4)
r := uint32(hiI) - ((g % uint32(ran4)) << 2)
switch d {
case 0:
return r, r, r, uint32(0xffff)
case 1:
return r, 0, 0, uint32(0xffff)
case 2:
return 0, r, 0, uint32(0xffff)
default:
return 0, 0, r, uint32(0xffff)
}
} else {
g := uint32(hiI) - ((uint32(j) * uint32(ran)) / uint32(y-2*inf))
return g, g, g, uint32(0xffff)
}
}
// 2 histograms on the botton: scaled & absolute
cv := float64((y-j)-1) / finf
ncv := cv * 2.
g := uint32(0xffff)
if cv < .5 {
hv := float64(histScaled[uint16(i)]) / maxHSF
if ncv >= hv {
g = uint32(0)
}
} else {
ncv -= 1.
hv2 := float64(histScaled2[uint16(i)]) / maxHSF2
if ncv >= hv2 {
g = uint32(0)
}
}
return g, g, g, uint32(0xffff)
}
}

dtEndH := time.Now()
timeH += dtEndH.Sub(dtStartH)
fmt.Printf(" %s: (%d, %d) int: (%d, %d) mult: %f...", colrgba, minGs, maxGs, loI, hiI, mult)
// info: fmt.Printf("histCum: %+v\n", histCum.str())
_ = flush.Flush()

che := make(chan error)
nThreads := 0
ctxa := []jpegbw.FparCtx{}
ctxInUse := make(map[int]bool)
for i := 0; i < thrN; i++ {
ctxa = append(ctxa, fctx[colidx].Cpy())
ctxInUse[i] = false
}

// calculations for current color
var cmtx = &sync.Mutex{}
dtStartF := time.Now()
for ii := 0; ii < x; ii++ {
go func(c chan error, i int) {
// debug: fmt.Printf("line: %d/%d\n", i, x)
cmtx.Lock()
cNum := -1
for t := 0; t < thrN; t++ {
if !ctxInUse[t] {
cNum = t
ctxInUse[cNum] = true
break
}
}
cmtx.Unlock()
if cNum < 0 {
// Sync
c <- fmt.Errorf("no context copy available: i=%d", i)
return
}
fi := float64(i) / float64(x)
trace := 1.0
for j := 0; j < y; j++ {
fj := float64(j) / float64(y)
pr, pg, pb, pa := getPixelFunc(&m, i, j)
//if inf > 0 && (i >= xo || j >= yo) {
if inf > 0 && j >= yo {
switch colidx {
case 0:
pxdata[i][j][colidx] = uint16(pr)
case 1:
pxdata[i][j][colidx] = uint16(pg)
case 2:
pxdata[i][j][colidx] = uint16(pb)
default:
pxdata[i][j][colidx] = uint16(pa)
}
continue
}
gs := uint16(r*float64(pr) + g*float64(pg) + b*float64(pb))
iv := int(gs) - int(loI)
if iv < 0 {
iv = 0
}
fv := float64(iv) * mult
if fv > 65535.0 {
fv = 65535.0
}
if gaB {
fv = math.Pow(fv/65535.0, ga) * 65535.0
if fv < 0.0 {
fv = 0.0
}
if fv > 65535.0 {
fv = 65535.0
}
}
if bFun[colidx] {
var e error
cv, e := ctxa[cNum].FparF(
[]complex128{
complex(fv/65535.0, 0.0),
complex(fi, fj),
complex(float64(pr)/65535.0, float64(pg)/65535.0),
complex(float64(pb)/65535.0, float64(pa)/65535.0),
complex(fk, trace),
},
)
if e != nil {
// Sync
cmtx.Lock()
ctxInUse[cNum] = false
cmtx.Unlock()
c <- e
return
}
if useImag[colidx] {
fv = imag(cv)
} else {
fv = real(cv)
}
trace = fv
// trace: fmt.Printf("trace is: %v\n", trace)
fv *= 65535.0
if fv < 0.0 {
fv = 0.0
}
if fv > 65535.0 {
fv = 65535.0
}
}
pxdata[i][j][colidx] = uint16(fv)
}
// Sync
cmtx.Lock()
ctxInUse[cNum] = false
cmtx.Unlock()
c <- nil
}(che, ii)

// Keep maximum number of threads
nThreads++
if nThreads == thrN {
e := <-che
if e != nil {
return e
}
nThreads--
}
}
for nThreads > 0 {
e := <-che
if e != nil {
return e
}
nThreads--
}
dtEndF := time.Now()
timeF += dtEndF.Sub(dtStartF)
}

```

Leave a reaction on this issue to contribute to the project by classifying this instance as a **Bug** :-1:, **Mitigated** :+1:, or **Desirable Behavior** :rocket:
See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: 1e2480f4449a7db41c44100807e88c25855e97b3