why this glsl shader isn't working on hdr content?

[geextahslex]

Hi. Do you know why this works on SDR but isn't on HDR? The original shader worked on both and only 3 lines of code have changed... I marked them at the end

//!PARAM vibr
//!DESC Saturates/deSaturates
//!TYPE float
//!MINIMUM -1
-0.5

//!HOOK MAIN
//!BIND HOOKED
//!DESC Vibrance

#define CoefLuma vec4(0.2126, 0.7152, 0.0722, 0) //sRGB, HDTV
float Thresh = 200.0/255.0;
float w = 10.0/255.0;

vec4 hook() {
    vec4 c0 = HOOKED_texOff(0);
    float lum = (c0.r + c0.g + c0.b)/3.0;

    float colorSat = max(max(c0.r, c0.g), c0.b) - min(min(c0.r, c0.g), c0.b); 
    vec3 sat = mix(vec3(dot(c0, CoefLuma)), c0.rgb, 1+vibr - colorSat*abs(vibr));
    float delta = smoothstep(Thresh-w, Thresh+w, lum);
1   sat = mix(sat, c0.rgb, delta);
2   delta = smoothstep(0.8, 0.9, colorSat);
3   c0.rgb = mix(c0.rgb, sat, delta);
    return c0;
}

[bjin]

not related