R20 note on BEAM file format: compact term encoding

nonblockio · Oct 6, 2017 · 1ebae17 · 1ebae17
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diff --git a/chapters/beam_modules.asciidoc b/chapters/beam_modules.asciidoc
@@ -513,6 +513,8 @@ The reason behind this complicated design is to try and fit as much type and val
 
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+NOTE: Since OTP 20 this tag format has been changed and the `Extended - Float` is gone. All following tag values are shifted down by 1: List is 2#10111, fpreg is 2#100111, alloc list is 2#110111 and literal is 2#1010111. Floating point values now go straight to literal area of the BEAM file.
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 It uses the first 3 bits of a first byte to store the tag which defines the type of the following value. If the bits were all 1 (special value 7 or ?tag_z from `beam_opcodes.hrl`), then a few more bits are used.
 
 For values under 16, the value is placed entirely into bits 4-5-6-7 having bit 3 set to 0: