The description of the %a/%A specifiers in the printf(3) man page could stand some improvement. In particular, it is not clear from the current (6.9.1) document what base is used for the "p±d" part of the format. Furthermore, the description refers to a "decimal point", even though it would be better referred to as the "radix point", as the number in question is not a decimal representation. It can be inferred from the nature of %a that the base should be a power of two. and it can be further inferred from the nature of hexadecimal floating-point literals in C (as specified by C99 and later) that the base must exactly be the number two, but it would be helpful for the printf(3) man page to state this explicitly. My first expectation when reading the man page was that the exponent would be taken in base 16; my second thought is that it is base FLT_RADIX (which is 2 on IEEE 754 floating-point systems, but 16 on S/390). Only by going back to the standard and reading carefully could I determine that the exponent in p-notation must always be taken from a base of 2. A patch with one suggested wording is attached. The entry for "a, A" in https://pubs.opengroup.org/onlinepubs/9699919799/functions/printf.html gives an even better rewording, though I suspect there would be copyright issues in simply copying its text. --Ken Pizzini
--- printf.3~ 2024-11-13 01:07:23.023847047 -0800 +++ printf.3 2024-11-13 01:55:48.368341811 -0800 @@ -757,15 +757,18 @@ the letters ABCDEF, and the exponent separator .B P is used. -There is one hexadecimal digit before the decimal point, +There is one hexadecimal digit before the radix point, and the number of digits after it is equal to the precision. The default precision suffices for an exact representation of the value if an exact representation in base 2 exists and otherwise is sufficiently large to distinguish values of type .IR double . -The digit before the decimal point is unspecified for nonnormalized +The digit before the radix point is unspecified for nonnormalized numbers, and nonzero but otherwise unspecified for normalized numbers. -The exponent always contains at least one +The exponent +.IR d , +which is the appropriate exponent of 2 expressed as a decimal integer, +always contains at least one digit; if the value is zero, the exponent is 0. .TP .B c
