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perf: improve small size fft #791

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Merged
gbotrel merged 1 commit into from
Jan 9, 2026
+181 −2
Merged

perf: improve small size fft #791

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59 changes: 59 additions & 0 deletions field/babybear/fft/fft.go
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59 changes: 59 additions & 0 deletions field/koalabear/fft/fft.go
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65 changes: 63 additions & 2 deletions internal/generator/field/template/fft/fft.go.tmpl
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Original file line number Diff line number Diff line change
Expand Up @@ -218,7 +218,13 @@ func difFFT(a []{{ .FF }}.Element, w {{ .FF }}.Element, twiddles [][]{{ .FF }}.E
kerDIFNP_{{$ksize}}(a, twiddles, stage-twiddlesStartStage)
return
}
{{- end }}
{{- end }}{{- if .HasASMKernel}} else if n == 512 {
kerDIFNP_512(a, twiddles, stage-twiddlesStartStage)
return
} else if n == 1024 {
kerDIFNP_1024(a, twiddles, stage-twiddlesStartStage)
return
}{{- end}}
}
m := n >> 1

Expand Down Expand Up @@ -312,7 +318,13 @@ func ditFFT(a []{{ .FF }}.Element, w {{ .FF }}.Element, twiddles [][]{{ .FF }}.E
kerDITNP_{{$ksize}}(a, twiddles, stage-twiddlesStartStage)
return
}
{{- end }}
{{- end }}{{- if .HasASMKernel}} else if n == 512 {
kerDITNP_512(a, twiddles, stage-twiddlesStartStage)
return
} else if n == 1024 {
kerDITNP_1024(a, twiddles, stage-twiddlesStartStage)
return
}{{- end}}
}

m := n >> 1
Expand Down Expand Up @@ -397,6 +409,55 @@ func innerDITWithoutTwiddles(a []{{ .FF }}.Element, at, w {{ .FF }}.Element, sta
{{genKernel $.FF $ksize $klog2}}
{{end}}

{{- if .HasASMKernel}}
// kerDIFNP_512 is an optimized 512-element DIF kernel that avoids recursion overhead
// by directly processing the outer butterfly layer and then calling the 256-element kernel.
func kerDIFNP_512(a []{{ .FF }}.Element, twiddles [][]{{ .FF }}.Element, stage int) {
// Stage 0: butterfly with m=256
innerDIFWithTwiddles(a, twiddles[stage], 0, 256, 256)
// Process two halves with the 256-element kernel
kerDIFNP_256(a[:256], twiddles, stage+1)
kerDIFNP_256(a[256:], twiddles, stage+1)
}

// kerDITNP_512 is an optimized 512-element DIT kernel that avoids recursion overhead.
func kerDITNP_512(a []{{ .FF }}.Element, twiddles [][]{{ .FF }}.Element, stage int) {
// Process two halves with the 256-element kernel first (DIT order)
kerDITNP_256(a[:256], twiddles, stage+1)
kerDITNP_256(a[256:], twiddles, stage+1)
// Final stage: butterfly with m=256
innerDITWithTwiddles(a, twiddles[stage], 0, 256, 256)
}

// kerDIFNP_1024 is an optimized 1024-element DIF kernel that avoids recursion overhead.
func kerDIFNP_1024(a []{{ .FF }}.Element, twiddles [][]{{ .FF }}.Element, stage int) {
// Stage 0: butterfly with m=512
innerDIFWithTwiddles(a, twiddles[stage], 0, 512, 512)
// Stage 1: butterfly with m=256 on both halves
innerDIFWithTwiddles(a[:512], twiddles[stage+1], 0, 256, 256)
innerDIFWithTwiddles(a[512:], twiddles[stage+1], 0, 256, 256)
// Process four quarters with the 256-element kernel
kerDIFNP_256(a[:256], twiddles, stage+2)
kerDIFNP_256(a[256:512], twiddles, stage+2)
kerDIFNP_256(a[512:768], twiddles, stage+2)
kerDIFNP_256(a[768:], twiddles, stage+2)
}

// kerDITNP_1024 is an optimized 1024-element DIT kernel that avoids recursion overhead.
func kerDITNP_1024(a []{{ .FF }}.Element, twiddles [][]{{ .FF }}.Element, stage int) {
// Process four quarters with the 256-element kernel first (DIT order)
kerDITNP_256(a[:256], twiddles, stage+2)
kerDITNP_256(a[256:512], twiddles, stage+2)
kerDITNP_256(a[512:768], twiddles, stage+2)
kerDITNP_256(a[768:], twiddles, stage+2)
// Stage 1: butterfly with m=256 on both halves
innerDITWithTwiddles(a[:512], twiddles[stage+1], 0, 256, 256)
innerDITWithTwiddles(a[512:], twiddles[stage+1], 0, 256, 256)
// Final stage: butterfly with m=512
innerDITWithTwiddles(a, twiddles[stage], 0, 512, 512)
}
{{- end}}

{{define "genKernel FF sizeKernel sizeKernelLog2"}}

func kerDIFNP_{{.sizeKernel}}generic(a []{{ .FF }}.Element, twiddles [][]{{ .FF }}.Element, stage int) {
Expand Down
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