On Fri, Mar 15, 2019 at 12:38:59PM -0700, Guenter Roeck wrote: > On Fri, Mar 15, 2019 at 11:29:45AM -0700, Guenter Roeck wrote: > > On Fri, Mar 15, 2019 at 10:19:33AM +0000, Grönke, Christian wrote: > > > Hello Guenter, > > > > > > > -----Ursprüngliche Nachricht----- > > > > Von: Guenter Roeck <groeck7@xxxxxxxxx> Im Auftrag von Guenter Roeck > > > > Gesendet: Donnerstag, 14. März 2019 17:53 > > > > An: Grönke, Christian <C.Groenke@xxxxxxxxxx> > > > > Cc: linux-hwmon@xxxxxxxxxxxxxxx > > > > Betreff: Re: PMBus driver for FSP/3Y Power device with non-standard VOUT > > > > values (LINEAR11 vs LINEAR16) > > > > > > > > Hi Christian, > > > > On Thu, Mar 14, 2019 at 04:08:32PM +0000, Grönke, Christian wrote: > > > > > > > > > > The framework code seemed to work fine. I used your code for the > > > > conversion: > > > > > linear11 -> 'scaled integer' -> ieee754 It provided a way to test > > > > > the code and was easy for me as my tries to do some other bit magic > > > > > weren't successful. That means I partly tested the code from > > > > > pmbus_data2reg_ieee754 as my read_word function uses this for the > > > > > conversion. Of course not the module local function... > > > > > > > > > > > > > Wondering ... I would have thought that it should be possible to > > > > implement a simplified linear11 <--> ieee754 conversion, without > > > > converting to a scaled integer first. Have you tried that ? > > > > > > There might be a more efficient and elegant way. I toyed around with > > > the conversion for a moment but didn't figure out a working way > > > quickly. > > > > This should work. > > Somewhat optimized versions, with additional boundary checks, kernel types, and one less while loop. Guenter --- u16 lin2ieee(u16 lin11) { s16 mantissa = ((s16)((lin11 & 0x7ff) << 5)) >> 5; int exponent = (((s16)lin11) >> 11) + 25; u16 sign = 0; /* simple case */ if (mantissa == 0) return 0; if (mantissa < 0) { sign = 0x8000; mantissa = -mantissa; } while (mantissa < 0x400 && exponent > 1) { mantissa <<= 1; exponent--; } /* boundary checks */ if (exponent > 30) return sign | 0x7bff; if (mantissa < 0x400) return sign | 0x0400; return sign | (exponent << 10) | (mantissa & 0x3ff); } u16 ieee2lin(u16 ieee) { s16 mantissa = (ieee & 0x3ff) | 0x400; int exponent = ((ieee >> 10) & 0x1f); u16 sign = ieee & 0x8000; int shift; /* 0 or too small */ if (ieee == sign || exponent == 0) return 0; /* NaN */ if (exponent == 0x1f) return sign ? 0xffff : 0xfbff; exponent -= 25; /* map into lin11 number space */ mantissa >>= 1; exponent++; shift = -15 - exponent; if (shift > 0) { exponent = -15; mantissa >>= shift; } /* boundary checks */ if (mantissa == 0) /* number too small */ return 0; if (sign) mantissa = -mantissa; return (exponent << 11) | (mantissa & 0x7ff); }